autumn_web/

tls.rs

//! Inbound (server-side) TLS support (issue #1603).
//!
//! This module lets an Autumn app terminate HTTPS in-process, without a
//! sidecar reverse proxy, when `[server.tls]` names a certificate + key.
//! It provides five things:
//!
//! (`lib.rs` carries an outer doc comment on `pub mod tls`, which is merged
//! with this block, so every link below is fully qualified — a bare item name
//! would resolve in the crate root instead of here.)
//!
//! 1. **Fail-fast loading** — [`load_certified_key`](crate::tls::load_certified_key)
//!    reads the PEM cert chain and private key from disk, verifies they parse
//!    and that the private key matches the leaf certificate (rustls'
//!    [`CertifiedKey::from_der`](rustls::sign::CertifiedKey::from_der) compares
//!    `SubjectPublicKeyInfo`), and rejects an already-expired leaf certificate.
//!    Every error names the offending path so a misconfiguration is actionable.
//! 2. **A reloadable resolver** —
//!    [`ReloadableCertResolver`](crate::tls::ReloadableCertResolver) holds the
//!    current [`CertifiedKey`](rustls::sign::CertifiedKey) behind an `RwLock`
//!    and implements [`ResolvesServerCert`](rustls::server::ResolvesServerCert),
//!    so the certificate can be swapped atomically at runtime (e.g. after an
//!    ACME/`certbot` renewal) without dropping the listener or restarting the
//!    process.
//! 3. **Expiry inspection** — [`inspect_leaf`](crate::tls::inspect_leaf)
//!    returns the leaf certificate's `notAfter` so `autumn doctor` can warn on
//!    near-expiry and fail on an expired certificate, offline (no server boot,
//!    no network).
//! 4. **The listener** — [`TlsListener`](crate::tls::TlsListener) is the
//!    `axum::serve::Listener` the app binds when `[server.tls]` is set: it
//!    drives each rustls handshake off the accept loop, under a per-connection
//!    timeout, so neither a failed nor a stalled handshake can wedge the
//!    server.
//! 5. **Renewal** — [`CertReloader`](crate::tls::CertReloader) polls the
//!    cert/key mtimes and swaps the resolver's certificate when they change, so
//!    a `certbot`/ACME renewal is picked up without a restart.
//!
//! The crypto backend is `ring`, the SAME backend the outbound Postgres TLS
//! path already uses — the workspace deliberately forbids a second TLS backend
//! (no aws-lc-rs / native-tls / openssl).

// autumn-determinism-gate: production code in this module must read time and
// mint identifiers through the framework's injected seams (ClockSource /
// Entropy), never `Instant::now()` / `Utc::now()` / `SystemTime::now()` /
// `Uuid::new_v4()` directly. See CONTRIBUTING.md "Determinism seam gate"
// (issue #1797). The one exception is `now_unix` below: certificate validity
// is judged against real wall time by design, and it carries a per-site
// #[allow(clippy::disallowed_methods, reason = "…")].
#![cfg_attr(not(test), deny(clippy::disallowed_methods))]

use std::path::{Path, PathBuf};
use std::sync::{Arc, RwLock};

use rustls::crypto::CryptoProvider;
use rustls::server::{ClientHello, ResolvesServerCert};
use rustls::sign::CertifiedKey;
use rustls_pki_types::pem::PemObject as _;
use rustls_pki_types::{CertificateDer, PrivateKeyDer};

/// Default cert/key reload poll interval, in seconds.
///
/// The running server polls the cert and key file modification times this often
/// to detect an external renewal. 60s is frequent enough to pick up a
/// `certbot`/ACME renewal promptly while imposing a negligible
/// two-`stat`-per-minute cost.
pub const DEFAULT_RELOAD_INTERVAL_SECS: u64 = 60;

/// Something went wrong loading, validating, or inspecting the configured TLS
/// material. Every variant names the offending path so the operator can act on
/// it without guesswork.
#[derive(Debug, thiserror::Error)]
pub enum TlsError {
    /// The certificate file could not be read.
    #[error("failed to read TLS certificate file `{path}`: {source}")]
    ReadCert {
        /// Path that failed to read.
        path: PathBuf,
        /// Underlying I/O error.
        source: std::io::Error,
    },
    /// The private key file could not be read.
    #[error("failed to read TLS private key file `{path}`: {source}")]
    ReadKey {
        /// Path that failed to read.
        path: PathBuf,
        /// Underlying I/O error.
        source: std::io::Error,
    },
    /// The certificate PEM could not be parsed.
    #[error("failed to parse a PEM certificate in `{path}`: {source}")]
    ParseCert {
        /// Path whose PEM failed to parse.
        path: PathBuf,
        /// Underlying PEM parse error.
        source: rustls_pki_types::pem::Error,
    },
    /// No `CERTIFICATE` PEM block was present in the certificate file.
    #[error("no certificates found in `{path}` (expected at least one PEM CERTIFICATE block)")]
    NoCertificates {
        /// Path that contained no certificate.
        path: PathBuf,
    },
    /// The private key PEM could not be parsed.
    #[error("failed to parse a PEM private key in `{path}`: {source}")]
    ParseKey {
        /// Path whose PEM failed to parse.
        path: PathBuf,
        /// Underlying PEM parse error.
        source: rustls_pki_types::pem::Error,
    },
    /// The private key is unusable, or it does not match the leaf certificate.
    #[error(
        "the TLS private key `{key}` is invalid or does not match the leaf certificate `{cert}`: \
         {source}"
    )]
    InvalidKeyPair {
        /// Certificate path.
        cert: PathBuf,
        /// Key path.
        key: PathBuf,
        /// Underlying rustls error.
        source: Box<rustls::Error>,
    },
    /// The leaf certificate DER could not be parsed for expiry inspection.
    #[error("failed to parse the leaf certificate in `{path}` for expiry inspection: {detail}")]
    ParseLeaf {
        /// Certificate path.
        path: PathBuf,
        /// Human-readable parse detail.
        detail: String,
    },
    /// A certificate in the chain (at 1-based `position`) is not valid DER.
    ///
    /// The PEM block decoded, but the bytes are not a parseable X.509
    /// certificate — a malformed intermediate that rustls would store unparsed
    /// and serve to clients that reject the chain.
    #[error("certificate #{position} in the chain in `{path}` is malformed: {detail}")]
    ParseChainCert {
        /// Certificate path.
        path: PathBuf,
        /// 1-based position of the offending certificate in the chain.
        position: usize,
        /// Human-readable parse detail.
        detail: String,
    },
    /// The leaf certificate has already expired.
    #[error("the leaf certificate in `{path}` expired at {not_after} (UNIX {not_after_unix})")]
    Expired {
        /// Certificate path.
        path: PathBuf,
        /// RFC 2822-ish rendering of `notAfter`.
        not_after: String,
        /// `notAfter` as a UNIX timestamp.
        not_after_unix: i64,
    },
    /// The leaf certificate is not yet valid — its `notBefore` is in the future.
    #[error(
        "the leaf certificate in `{path}` is not valid until {not_before} (UNIX {not_before_unix})"
    )]
    NotYetValid {
        /// Certificate path.
        path: PathBuf,
        /// RFC 2822-ish rendering of `notBefore`.
        not_before: String,
        /// `notBefore` as a UNIX timestamp.
        not_before_unix: i64,
    },
    /// A non-leaf certificate in the chain (at 1-based `position`) has already
    /// expired. Normal TLS clients reject the whole chain during path
    /// validation, so refuse it at load/inspection time rather than boot a
    /// listener that serves it. Symmetric to the leaf's [`Self::Expired`].
    #[error(
        "certificate #{position} in the chain in `{path}` expired at {not_after} \
         (UNIX {not_after_unix})"
    )]
    ExpiredChainCert {
        /// Certificate path.
        path: PathBuf,
        /// 1-based position of the offending certificate in the chain.
        position: usize,
        /// RFC 2822-ish rendering of `notAfter`.
        not_after: String,
        /// `notAfter` as a UNIX timestamp.
        not_after_unix: i64,
    },
    /// A non-leaf certificate in the chain (at 1-based `position`) is not yet
    /// valid — its `notBefore` is in the future. Symmetric to the leaf's
    /// [`Self::NotYetValid`].
    #[error(
        "certificate #{position} in the chain in `{path}` is not yet valid until {not_before} \
         (UNIX {not_before_unix})"
    )]
    NotYetValidChainCert {
        /// Certificate path.
        path: PathBuf,
        /// 1-based position of the offending certificate in the chain.
        position: usize,
        /// RFC 2822-ish rendering of `notBefore`.
        not_before: String,
        /// `notBefore` as a UNIX timestamp.
        not_before_unix: i64,
    },
    /// Building the rustls `ServerConfig` failed.
    #[error("failed to build the rustls server configuration: {source}")]
    BuildConfig {
        /// Underlying rustls error.
        source: rustls::Error,
    },
    /// The mTLS client-CA bundle could not be read (issue #1640).
    #[error("failed to read the mTLS client CA bundle `{path}`: {source}")]
    ReadClientCa {
        /// Path that failed to read.
        path: PathBuf,
        /// Underlying I/O error.
        source: std::io::Error,
    },
    /// The mTLS client-CA bundle is not parseable PEM.
    #[error("failed to parse a PEM certificate in the mTLS client CA bundle `{path}`: {source}")]
    ParseClientCa {
        /// Path whose PEM failed to parse.
        path: PathBuf,
        /// Underlying PEM parse error.
        source: rustls_pki_types::pem::Error,
    },
    /// The mTLS client-CA bundle contains no certificate.
    #[error(
        "no CAs found in the mTLS client CA bundle `{path}` (expected at least one PEM \
         CERTIFICATE block)"
    )]
    NoClientCas {
        /// Path that contained no certificate.
        path: PathBuf,
    },
    /// A certificate in the bundle (at 1-based `position`) is not usable as a
    /// trust anchor.
    #[error(
        "CA #{position} in the mTLS client CA bundle `{path}` is not a valid trust anchor: {source}"
    )]
    InvalidClientCa {
        /// Bundle path.
        path: PathBuf,
        /// 1-based position of the offending certificate in the bundle.
        position: usize,
        /// Underlying rustls error.
        source: Box<rustls::Error>,
    },
    /// The mTLS revocation list could not be read.
    #[error("failed to read the mTLS revocation list `{path}`: {source}")]
    ReadCrl {
        /// Path that failed to read.
        path: PathBuf,
        /// Underlying I/O error.
        source: std::io::Error,
    },
    /// The mTLS revocation list is not parseable PEM.
    #[error("failed to parse a PEM block in the mTLS revocation list `{path}`: {source}")]
    ParseCrl {
        /// Path whose PEM failed to parse.
        path: PathBuf,
        /// Underlying PEM parse error.
        source: rustls_pki_types::pem::Error,
    },
    /// The mTLS revocation list contains no CRL.
    #[error("no revocation list found in `{path}` (expected at least one PEM X509 CRL block)")]
    NoCrls {
        /// Path that contained no CRL.
        path: PathBuf,
    },
    /// A CRL in the file (at 1-based `position`) is not valid DER.
    #[error("CRL #{position} in `{path}` is malformed: {detail}")]
    ParseCrlDer {
        /// Revocation-list path.
        path: PathBuf,
        /// 1-based position of the offending CRL in the file.
        position: usize,
        /// Human-readable parse detail.
        detail: String,
    },
    /// The mTLS revocation list does not cover every CA in the client-CA
    /// bundle: no CRL in the file is issued by one or more of the bundle's
    /// CAs (issue #2706).
    ///
    /// Once any CRL is configured, rustls denies handshakes whose revocation
    /// status is *unknown*, so clients presenting certificates issued by an
    /// uncovered CA are refused even though their CA is trusted — the
    /// availability trap in the CA rotation `docs/guide/tls.md` documents
    /// (old + new CA in one bundle, CRL published for the old one first).
    /// Publish a CRL for each CA in the bundle (or remove the uncovered CA)
    /// before starting with a CRL configured.
    #[error(
        "the mTLS revocation list `{crl_path}` has no CRL issued by {uncovered:?} \
         from the client CA bundle `{ca_bundle_path}`; once any CRL is configured, \
         rustls refuses handshakes whose revocation status is unknown, so these \
         CAs' clients would be rejected — publish a CRL for each CA in the \
         bundle or remove the uncovered CA"
    )]
    CrlCoverageGap {
        /// CA bundle path.
        ca_bundle_path: PathBuf,
        /// CRL path.
        crl_path: PathBuf,
        /// Subject DNs of the CAs no CRL in the file is issued by.
        uncovered: Vec<String>,
    },
    /// Building the rustls client-certificate verifier failed.
    #[error("failed to build the mTLS client certificate verifier: {source}")]
    BuildClientVerifier {
        /// Underlying rustls error.
        source: rustls::server::VerifierBuilderError,
    },
    /// A verified peer certificate could not be parsed into an identity.
    #[error("failed to parse the verified client certificate: {detail}")]
    ParsePeerCert {
        /// Human-readable parse detail.
        detail: String,
    },
}

/// Mutual-TLS client-certificate verification (issue #1640).
pub mod client_auth;

/// The `ring` crypto provider used for all inbound TLS. Built once per call;
/// callers that build many configs should cache the returned `Arc`.
#[must_use]
pub fn crypto_provider() -> Arc<CryptoProvider> {
    Arc::new(rustls::crypto::ring::default_provider())
}

/// Read and PEM-decode the certificate chain at `cert_path`.
fn read_cert_chain(cert_path: &Path) -> Result<Vec<CertificateDer<'static>>, TlsError> {
    let pem = std::fs::read(cert_path).map_err(|source| TlsError::ReadCert {
        path: cert_path.to_path_buf(),
        source,
    })?;
    let mut chain = Vec::new();
    for cert in CertificateDer::pem_slice_iter(&pem) {
        let cert = cert.map_err(|source| TlsError::ParseCert {
            path: cert_path.to_path_buf(),
            source,
        })?;
        chain.push(cert);
    }
    if chain.is_empty() {
        return Err(TlsError::NoCertificates {
            path: cert_path.to_path_buf(),
        });
    }
    Ok(chain)
}

/// Read and PEM-decode the private key at `key_path`.
fn read_private_key(key_path: &Path) -> Result<PrivateKeyDer<'static>, TlsError> {
    let pem = std::fs::read(key_path).map_err(|source| TlsError::ReadKey {
        path: key_path.to_path_buf(),
        source,
    })?;
    PrivateKeyDer::from_pem_slice(&pem).map_err(|source| TlsError::ParseKey {
        path: key_path.to_path_buf(),
        source,
    })
}

/// The `notBefore` and `notAfter` of the leaf certificate, as UNIX timestamps
/// (seconds), returned as `(not_before, not_after)`.
///
/// Parses just enough of the DER to read the validity window; a parse failure
/// is surfaced rather than silently ignored so a corrupt certificate is caught
/// at load time.
fn leaf_validity_unix(cert_path: &Path, leaf: &CertificateDer<'_>) -> Result<(i64, i64), TlsError> {
    use x509_parser::prelude::FromDer as _;

    let (_, parsed) =
        x509_parser::certificate::X509Certificate::from_der(leaf.as_ref()).map_err(|e| {
            TlsError::ParseLeaf {
                path: cert_path.to_path_buf(),
                detail: e.to_string(),
            }
        })?;
    let validity = parsed.validity();
    Ok((
        validity.not_before.timestamp(),
        validity.not_after.timestamp(),
    ))
}

/// Parse and lifetime-check every NON-leaf certificate DER in `chain`, failing
/// fast (naming the 1-based chain position) if any block is not a parseable
/// X.509 certificate OR is outside its validity window at `now_unix`.
///
/// [`read_cert_chain`] only PEM-decodes each block, and rustls'
/// [`CertifiedKey::from_der`] validates only the leaf (`chain[0]`). A malformed
/// — or an expired / not-yet-valid — INTERMEDIATE would therefore be stored
/// unchecked and served, so startup and `autumn doctor` pass while normal TLS
/// clients reject the chain during path validation. Parsing and lifetime-
/// checking each intermediate here turns that into an actionable fail-fast at
/// load/inspection time. The leaf (`chain[0]`) is parsed and lifetime-checked
/// separately (by [`leaf_validity_unix`] and its callers).
///
/// `now_unix` is the current UNIX time; it is a parameter (rather than read
/// internally) so tests can pin "now" deterministically.
fn validate_chain_certs(
    cert_path: &Path,
    chain: &[CertificateDer<'_>],
    now_unix: i64,
) -> Result<(), TlsError> {
    use x509_parser::prelude::FromDer as _;

    // Skip index 0 (the leaf); its DER and validity window are checked by the
    // callers via `leaf_validity_unix`.
    for (idx, cert) in chain.iter().enumerate().skip(1) {
        // 1-based, matching how operators count "certificate #2" in a bundle.
        let position = idx + 1;
        let (_, parsed) = x509_parser::certificate::X509Certificate::from_der(cert.as_ref())
            .map_err(|e| TlsError::ParseChainCert {
                path: cert_path.to_path_buf(),
                position,
                detail: e.to_string(),
            })?;

        // Reject an intermediate outside its validity window, mirroring the
        // leaf's not-yet-valid / expired handling: `notBefore` in the future is
        // as fatal as a past `notAfter`, since either makes clients reject the
        // served chain.
        let validity = parsed.validity();
        let not_before = validity.not_before.timestamp();
        let not_after = validity.not_after.timestamp();
        if now_unix < not_before {
            return Err(TlsError::NotYetValidChainCert {
                path: cert_path.to_path_buf(),
                position,
                not_before: render_unix(not_before),
                not_before_unix: not_before,
            });
        }
        if not_after < now_unix {
            return Err(TlsError::ExpiredChainCert {
                path: cert_path.to_path_buf(),
                position,
                not_after: render_unix(not_after),
                not_after_unix: not_after,
            });
        }
    }
    Ok(())
}

/// Load, validate, and return the certificate + key as a rustls [`CertifiedKey`].
///
/// Fails fast on any of: missing/unreadable file, unparseable PEM, an empty
/// certificate file, a private key that does not match the leaf certificate, or
/// an already-expired leaf certificate.
///
/// `now_unix` is the current UNIX time; it is a parameter (rather than read
/// internally) so tests can pin "now" deterministically.
///
/// # Errors
///
/// Returns a [`TlsError`] describing the first problem encountered.
pub fn load_certified_key(
    cert_path: &Path,
    key_path: &Path,
    provider: &CryptoProvider,
    now_unix: i64,
) -> Result<Arc<CertifiedKey>, TlsError> {
    let chain = read_cert_chain(cert_path)?;
    let key = read_private_key(key_path)?;

    // Reject a leaf outside its validity window before we even build the key:
    // an expired OR not-yet-valid certificate fails every client handshake, so
    // refuse at startup with a clear message rather than booting into a broken
    // listener. Symmetric bounds: `notBefore` in the future is as fatal as a
    // past `notAfter`.
    let (not_before, not_after) = leaf_validity_unix(cert_path, &chain[0])?;
    if now_unix < not_before {
        return Err(TlsError::NotYetValid {
            path: cert_path.to_path_buf(),
            not_before: render_unix(not_before),
            not_before_unix: not_before,
        });
    }
    if not_after < now_unix {
        return Err(TlsError::Expired {
            path: cert_path.to_path_buf(),
            not_after: render_unix(not_after),
            not_after_unix: not_after,
        });
    }

    // Parse and lifetime-check every intermediate before accepting the chain:
    // rustls validates only the leaf, so a malformed — or expired / not-yet-valid
    // — intermediate would otherwise boot a listener that serves a chain normal
    // clients reject during path validation.
    validate_chain_certs(cert_path, &chain, now_unix)?;

    // `from_der` loads the key with the crypto provider (rejecting an invalid
    // key) and compares the key's SubjectPublicKeyInfo against the leaf
    // certificate's, so a cert/key mismatch is caught here.
    let certified = CertifiedKey::from_der(chain, key, provider).map_err(|source| {
        TlsError::InvalidKeyPair {
            cert: cert_path.to_path_buf(),
            key: key_path.to_path_buf(),
            source: Box::new(source),
        }
    })?;

    Ok(Arc::new(certified))
}

/// Render a UNIX timestamp as a UTC string for error messages. Falls back to
/// the raw timestamp if it is out of range for the formatter.
fn render_unix(secs: i64) -> String {
    x509_parser::time::ASN1Time::from_timestamp(secs)
        .ok()
        .map_or_else(|| format!("UNIX {secs}"), |t| t.to_string())
}

/// A [`ResolvesServerCert`] whose certificate can be swapped at runtime.
///
/// Every TLS handshake takes a short read lock to clone the current
/// `Arc<CertifiedKey>`; a reload swaps in a new `Arc` under a brief write lock.
/// Readers never block each other, and a reload never interrupts an in-flight
/// handshake — it only affects handshakes that start after the swap.
#[derive(Debug)]
pub struct ReloadableCertResolver {
    current: RwLock<Arc<CertifiedKey>>,
}

impl ReloadableCertResolver {
    /// Create a resolver serving `initial`.
    #[must_use]
    pub const fn new(initial: Arc<CertifiedKey>) -> Self {
        Self {
            current: RwLock::new(initial),
        }
    }

    /// Atomically replace the served certificate.
    pub fn store(&self, next: Arc<CertifiedKey>) {
        let mut guard = self
            .current
            .write()
            .unwrap_or_else(std::sync::PoisonError::into_inner);
        *guard = next;
    }

    /// Snapshot the currently served certificate.
    #[must_use]
    pub fn current(&self) -> Arc<CertifiedKey> {
        let guard = self
            .current
            .read()
            .unwrap_or_else(std::sync::PoisonError::into_inner);
        Arc::clone(&guard)
    }
}

impl ResolvesServerCert for ReloadableCertResolver {
    fn resolve(&self, _client_hello: ClientHello<'_>) -> Option<Arc<CertifiedKey>> {
        Some(self.current())
    }
}

/// Build the rustls [`ServerConfig`](rustls::ServerConfig) that terminates
/// inbound TLS, backed by `resolver` so the certificate stays swappable.
///
/// Advertises ALPN `[b"h2", b"http/1.1"]` (#2321) so browsers negotiate
/// HTTP/2; ALPN-less and http/1.1-only clients are unaffected.
///
/// # Errors
///
/// Returns [`TlsError::BuildConfig`] if rustls rejects the chosen protocol
/// versions for the provider.
pub fn build_server_config(
    provider: Arc<CryptoProvider>,
    resolver: Arc<ReloadableCertResolver>,
) -> Result<Arc<rustls::ServerConfig>, TlsError> {
    build_server_config_with_resolver(provider, resolver)
}

/// [`build_server_config`], for any [`ResolvesServerCert`].
///
/// The custom-domain path (#1635) serves a per-SNI resolver rather than the
/// single swappable certificate, so the listener takes the resolver as a trait
/// object; everything else about the config is identical — including the
/// ALPN `[b"h2", b"http/1.1"]` advertisement (#2321).
///
/// # Errors
///
/// Returns [`TlsError::BuildConfig`] if rustls rejects the chosen protocol
/// versions for the provider.
pub fn build_server_config_with_resolver(
    provider: Arc<CryptoProvider>,
    resolver: Arc<dyn ResolvesServerCert>,
) -> Result<Arc<rustls::ServerConfig>, TlsError> {
    build_server_config_with_client_auth(provider, resolver, None)
}

/// [`build_server_config_with_resolver`], additionally verifying client
/// certificates against `client_verifier` (issue #1640).
///
/// `None` takes the identical `with_no_client_auth()` path as before, so a
/// deployment with no `[server.tls.client_auth]` section handshakes exactly as
/// it did under #1603 — apart from the ALPN `[b"h2", b"http/1.1"]`
/// advertisement (#2321), which both arms set identically.
///
/// # Errors
///
/// Returns [`TlsError::BuildConfig`] if rustls rejects the chosen protocol
/// versions for the provider.
pub fn build_server_config_with_client_auth(
    provider: Arc<CryptoProvider>,
    resolver: Arc<dyn ResolvesServerCert>,
    client_verifier: Option<Arc<dyn rustls::server::danger::ClientCertVerifier>>,
) -> Result<Arc<rustls::ServerConfig>, TlsError> {
    let builder = rustls::ServerConfig::builder_with_provider(provider)
        .with_safe_default_protocol_versions()
        .map_err(|source| TlsError::BuildConfig { source })?;
    let mut config = match client_verifier {
        Some(verifier) => {
            let mut config = builder
                .with_client_cert_verifier(verifier)
                .with_cert_resolver(resolver);
            // Turn OFF session resumption for a client-authenticating listener.
            //
            // rustls restores a resumed connection's `peer_certificates` from
            // the stored session and never calls the verifier again
            // (`server/tls13.rs`, `server/tls12.rs`). So a client whose CA was
            // rotated out — or whose certificate was just added to the CRL —
            // would keep reconnecting on a resumed session until it expired,
            // and would keep presenting a verified-looking identity to
            // handlers. That is the one hole a swap-the-verifier design cannot
            // close by swapping, because the check it swaps is not run.
            //
            // The cost is a full handshake per connection, which is the right
            // trade for a listener whose whole purpose is deciding who may
            // connect. Server-only TLS keeps resumption untouched.
            config.session_storage = Arc::new(rustls::server::NoServerSessionStorage {});
            config.send_tls13_tickets = 0;
            config
        }
        None => builder.with_no_client_auth().with_cert_resolver(resolver),
    };
    // Advertise ALPN (#2321). Without an `alpn_protocols` list rustls
    // completes the handshake with no protocol selected, so a browser (or
    // `curl --http2`) never sends the HTTP/2 preface and the serve path's
    // h2 half — `hyper_util::server::conn::auto` already speaks it — stays
    // dead code in practice. `h2` first, then `http/1.1`: ALPN-less and
    // http/1.1-only clients are unaffected, and a client offering only `h2`
    // negotiates it. Both TLS modes funnel through here (static
    // `[server.tls]` and the ACME path, #1608), as do both client-auth arms
    // above, so the advertisement is identical everywhere.
    config.alpn_protocols = vec![b"h2".to_vec(), b"http/1.1".to_vec()];
    Ok(Arc::new(config))
}

/// Connection info for a request served over the mTLS-capable HTTPS listener
/// (issue #1640).
///
/// axum's `into_make_service_with_connect_info::<C>` requires `C:
/// Connected<IncomingStream>`; this carries the peer `SocketAddr` — so the rest
/// of the serve stack behaves exactly as on plain TCP — plus the verified
/// client identity, when the handshake produced one.
///
/// The identity is parsed once per *connection*, not per request.
#[derive(Clone, Debug)]
pub struct TlsConnectInfo {
    /// The peer's TCP address, identical to the plain-TCP path's connect info.
    pub peer: std::net::SocketAddr,
    /// The verified client identity, when the peer presented a certificate that
    /// passed verification. Always `None` on a listener with client auth off.
    pub client: Option<Arc<client_auth::ClientIdentity>>,
}

impl axum::extract::connect_info::Connected<axum::serve::IncomingStream<'_, TlsListener>>
    for TlsConnectInfo
{
    fn connect_info(stream: axum::serve::IncomingStream<'_, TlsListener>) -> Self {
        Self::from_stream(stream.io(), *stream.remote_addr())
    }
}

/// The HTTPS serve path wraps its listener in `StopAcceptingOnShutdown` (see
/// `accept_drain`), so the connect info must be available for the wrapper too.
impl
    axum::extract::connect_info::Connected<
        axum::serve::IncomingStream<'_, crate::accept_drain::StopAcceptingOnShutdown<TlsListener>>,
    > for TlsConnectInfo
{
    fn connect_info(
        stream: axum::serve::IncomingStream<
            '_,
            crate::accept_drain::StopAcceptingOnShutdown<TlsListener>,
        >,
    ) -> Self {
        Self::from_stream(stream.io(), *stream.remote_addr())
    }
}

impl
    axum::extract::connect_info::Connected<
        crate::http_server::IncomingStream<
            '_,
            crate::accept_drain::StopAcceptingOnShutdown<TlsListener>,
        >,
    > for TlsConnectInfo
{
    fn connect_info(
        stream: crate::http_server::IncomingStream<
            '_,
            crate::accept_drain::StopAcceptingOnShutdown<TlsListener>,
        >,
    ) -> Self {
        Self::from_stream(stream.io(), *stream.remote_addr())
    }
}

impl TlsConnectInfo {
    fn from_stream(
        io: &tokio_rustls::server::TlsStream<tokio::net::TcpStream>,
        peer: std::net::SocketAddr,
    ) -> Self {
        // rustls exposes the peer chain only after a successful handshake, so
        // anything here has already passed the configured verifier — the parse
        // turns a verified certificate into a usable identity, it does not
        // decide trust.
        let client = io
            .get_ref()
            .1
            .peer_certificates()
            .and_then(<[rustls_pki_types::CertificateDer<'_>]>::first)
            .and_then(|leaf| match client_auth::ClientIdentity::from_der(leaf) {
                Ok(identity) => Some(Arc::new(identity)),
                Err(e) => {
                    // Verified but unparseable: drop the identity rather than
                    // fabricate one. Routes that require mTLS then reject.
                    tracing::warn!(peer = %peer, error = %e, "could not parse the verified client certificate");
                    None
                }
            });
        Self { peer, client }
    }
}

/// Upper bound on TLS handshakes running concurrently at any instant.
///
/// The background acceptor task acquires a permit from a semaphore of this size
/// before spawning each handshake, so a flood of connecting clients can never
/// spawn an unbounded number of handshake tasks: once this many are in flight
/// the acceptor parks on the next permit (still draining the kernel accept
/// queue's backlog as permits free up). 256 is a generous default for a single
/// listener; it could be made configurable later if a deployment needs to tune
/// the in-flight-handshake ceiling.
const MAX_CONCURRENT_HANDSHAKES: usize = 256;

/// A completed TLS stream, its peer, and its connection slot (when capped).
type ReadyConn = (
    tokio_rustls::server::TlsStream<tokio::net::TcpStream>,
    std::net::SocketAddr,
    Option<crate::http_server::Slot>,
);

/// Capacity of the channel carrying completed TLS streams to `accept`.
///
/// Bounded so a burst of successful handshakes that outruns axum's consumption
/// applies backpressure (a completed-handshake task parks on `send` while still
/// holding its semaphore permit) rather than buffering without limit.
const READY_CONN_CHANNEL_CAPACITY: usize = 1024;

/// A TLS-terminating [`axum::serve::Listener`] wrapping a
/// [`tokio::net::TcpListener`].
///
/// [`accept`](axum::serve::Listener::accept) yields a decrypted
/// [`TlsStream`](tokio_rustls::server::TlsStream) plus the peer's
/// [`SocketAddr`](std::net::SocketAddr). Because the peer address is a real TCP
/// `SocketAddr`, the rest of the serve stack — connect-info, trusted-proxy
/// resolution, graceful shutdown, SSE/WebSocket streaming — is identical to the
/// plain-TCP path; the only difference is the handshake performed here.
///
/// TCP-accept and the rustls handshake are **decoupled**: a background acceptor
/// task drains `tcp.accept()` and, for each connection, spawns a bounded
/// handshake task (bounded by this module's `MAX_CONCURRENT_HANDSHAKES`, which
/// is private) that performs the rustls
/// handshake and forwards the finished stream over a channel to `accept`. This
/// means a flood of silent or stalled clients cannot serialize the accept loop:
/// a client that opens TCP but never completes (or even starts) the handshake
/// occupies only its own handshake task (bounded by `handshake_timeout`), never
/// head-of-line-blocking the acceptance of the next connection. A failed
/// handshake (a plaintext or malformed client, an unsupported cipher, a dropped
/// connection) is logged at debug and dropped; it never affects the acceptor.
pub struct TlsListener {
    /// Completed streams from the background handshake tasks.
    rx: tokio::sync::mpsc::Receiver<ReadyConn>,
    /// Starts the acceptor, with the `server.http.max_connections` slots
    /// when set. Until then no TCP connection is accepted, so none can
    /// escape a cap installed after `new` (issue #3065). `None` once sent.
    start: Option<tokio::sync::oneshot::Sender<Option<Arc<tokio::sync::Semaphore>>>>,
    /// The `max_connections` slots `limit_connections` installed. The first
    /// `accept` starts the acceptor with them.
    cap: Option<Arc<tokio::sync::Semaphore>>,
    /// Where `accept` puts the slot of the stream it returns.
    handoff: Option<crate::http_server::SlotHandoff>,
    /// The bound address, captured before `tcp` moved into the acceptor task.
    local_addr: std::net::SocketAddr,
    /// Shutdown signal; also used to park `accept` once the acceptor has ended
    /// (channel closed) so axum's own graceful-shutdown future drives teardown.
    shutdown: tokio_util::sync::CancellationToken,
    #[cfg(test)]
    handshakes: Arc<tokio::sync::Semaphore>,
}

impl TlsListener {
    /// Wrap `tcp` so accepted connections are TLS-terminated with `config`,
    /// bounding each handshake by `handshake_timeout` (a stalled or silent
    /// client is dropped rather than starving other clients). `shutdown` ties
    /// the background acceptor task's lifetime to server shutdown.
    ///
    /// The acceptor starts at the first [`accept`](axum::serve::Listener::accept).
    /// Until then clients wait in the kernel backlog.
    ///
    /// # Panics
    ///
    /// Panics if `tcp.local_addr()` fails — the listener is already bound, so
    /// this is not expected in practice.
    #[must_use]
    pub fn new(
        tcp: tokio::net::TcpListener,
        config: Arc<rustls::ServerConfig>,
        handshake_timeout: std::time::Duration,
        shutdown: tokio_util::sync::CancellationToken,
    ) -> Self {
        let local_addr = tcp
            .local_addr()
            .expect("bound TLS listener must have a local address");
        let acceptor = tokio_rustls::TlsAcceptor::from(config);
        let (tx, rx) = tokio::sync::mpsc::channel(READY_CONN_CHANNEL_CAPACITY);
        let semaphore = Arc::new(tokio::sync::Semaphore::new(MAX_CONCURRENT_HANDSHAKES));
        let (start, started) = tokio::sync::oneshot::channel();
        let acceptor_shutdown = shutdown.clone();
        #[cfg(test)]
        let handshakes = Arc::clone(&semaphore);

        tokio::spawn(async move {
            let cap = tokio::select! {
                () = acceptor_shutdown.cancelled() => return,
                cap = started => match cap {
                    Ok(cap) => cap,
                    // The listener was dropped before it accepted.
                    Err(_) => return,
                },
            };
            run_acceptor(
                tcp,
                acceptor,
                handshake_timeout,
                semaphore,
                cap,
                tx,
                acceptor_shutdown,
            )
            .await;
        });

        Self {
            rx,
            start: Some(start),
            cap: None,
            handoff: None,
            local_addr,
            shutdown,
            #[cfg(test)]
            handshakes,
        }
    }

    /// Count at most `max` connections, from TCP accept to close. The
    /// acceptor still starts at the first `accept`, so an upgrade successor
    /// takes no connection before its server runs. Returns where `accept`
    /// puts the slot of each stream, for the serve loop. `None` when the
    /// acceptor already started: the cap can no longer cover every
    /// connection, so the serve loop keeps its own.
    pub(crate) fn limit_connections(
        &mut self,
        max: usize,
    ) -> Option<crate::http_server::SlotHandoff> {
        if self.start.is_none() || self.handoff.is_some() {
            return None;
        }
        let max = max.min(tokio::sync::Semaphore::MAX_PERMITS);
        self.cap = Some(Arc::new(tokio::sync::Semaphore::new(max)));
        let handoff = crate::http_server::SlotHandoff::default();
        self.handoff = Some(Arc::clone(&handoff));
        Some(handoff)
    }

    #[cfg(test)]
    fn handshakes_in_flight(&self) -> usize {
        MAX_CONCURRENT_HANDSHAKES - self.handshakes.available_permits()
    }
}

/// Take a connection slot, when the cap is set. `None` on shutdown.
async fn take_slot(
    cap: Option<&Arc<tokio::sync::Semaphore>>,
    shutdown: &tokio_util::sync::CancellationToken,
) -> Option<Option<crate::http_server::Slot>> {
    let Some(slots) = cap else {
        return Some(None);
    };
    tokio::select! {
        () = shutdown.cancelled() => None,
        permit = Arc::clone(slots).acquire_owned() => {
            permit.ok().map(|permit| Some(Box::new(permit) as crate::http_server::Slot))
        }
    }
}

/// Background accept loop: drain `tcp`, and for each connection spawn a bounded
/// handshake task that forwards the completed TLS stream over `tx`. Breaks (and
/// drops `tx`) on `shutdown`.
async fn run_acceptor(
    tcp: tokio::net::TcpListener,
    acceptor: tokio_rustls::TlsAcceptor,
    handshake_timeout: std::time::Duration,
    semaphore: Arc<tokio::sync::Semaphore>,
    cap: Option<Arc<tokio::sync::Semaphore>>,
    tx: tokio::sync::mpsc::Sender<ReadyConn>,
    shutdown: tokio_util::sync::CancellationToken,
) {
    loop {
        // At the connection cap, wait for a free slot before TCP accept.
        let Some(slot) = take_slot(cap.as_ref(), &shutdown).await else {
            break;
        };
        let (stream, peer) = tokio::select! {
            () = shutdown.cancelled() => break,
            result = tcp.accept() => match result {
                Ok(pair) => pair,
                Err(e) => {
                    // Never break the loop on a per-connection error — that
                    // would tear down the whole listener. Retry transient
                    // per-connection errors immediately; back off briefly on
                    // anything else so we do not spin (e.g. on the process's
                    // open-file limit).
                    if is_transient_connection_error(&e) {
                        continue;
                    }
                    tracing::error!(error = %e, "TLS listener accept error");
                    tokio::time::sleep(std::time::Duration::from_secs(1)).await;
                    continue;
                }
            },
        };

        // Acquire a permit BEFORE spawning so in-flight handshakes are bounded:
        // once `MAX_CONCURRENT_HANDSHAKES` are running, this parks (applying
        // backpressure to accept) until one finishes. The only error is a closed
        // semaphore, which we never close, so the `else` is unreachable in
        // practice; stop the loop defensively if it ever happens.
        let Ok(permit) = Arc::clone(&semaphore).acquire_owned().await else {
            break;
        };
        let acceptor = acceptor.clone();
        let tx = tx.clone();
        tokio::spawn(async move {
            // The permit is released when this task ends (handshake done,
            // failed, or timed out), freeing a slot for the next connection.
            let _permit = permit;
            // Bound the handshake so a client that connects but never sends a
            // ClientHello (or stalls mid-handshake) releases its permit instead
            // of holding it for the process lifetime.
            match tokio::time::timeout(handshake_timeout, acceptor.accept(stream)).await {
                Ok(Ok(tls)) => {
                    // A closed receiver means the listener is gone; drop.
                    let _ = tx.send((tls, peer, slot)).await;
                }
                Ok(Err(e)) => {
                    // An mTLS client-certificate rejection is an operator-facing
                    // event: counted by reason and logged at warn, rate-limited
                    // (#1640). Everything else keeps #1603's quiet debug line.
                    // The client sees only the standard TLS alert either way.
                    if !client_auth::record_handshake_rejection(&e, peer) {
                        tracing::debug!(
                            peer = %peer,
                            error = %e,
                            "TLS handshake failed; dropping connection"
                        );
                    }
                }
                Err(_elapsed) => {
                    tracing::debug!(peer = %peer, "TLS handshake timed out");
                }
            }
        });
    }
}

/// Whether an accept error is a per-connection condition (the client went away
/// between the kernel accept and ours) rather than a listener-wide one. These
/// are retried immediately; other errors (e.g. `EMFILE`) get a short backoff.
/// Mirrors axum's own built-in `TcpListener` accept behavior.
fn is_transient_connection_error(e: &std::io::Error) -> bool {
    matches!(
        e.kind(),
        std::io::ErrorKind::ConnectionRefused
            | std::io::ErrorKind::ConnectionAborted
            | std::io::ErrorKind::ConnectionReset
    )
}

impl axum::serve::Listener for TlsListener {
    type Io = tokio_rustls::server::TlsStream<tokio::net::TcpStream>;
    type Addr = std::net::SocketAddr;

    async fn accept(&mut self) -> (Self::Io, Self::Addr) {
        if let Some(start) = self.start.take() {
            // Start the acceptor, with the cap when one was installed.
            let _ = start.send(self.cap.take());
        }
        if let Some((tls, peer, slot)) = self.rx.recv().await {
            if let Some(handoff) = &self.handoff {
                *handoff
                    .lock()
                    .unwrap_or_else(std::sync::PoisonError::into_inner) = slot;
            }
            return (tls, peer);
        }
        // The acceptor task has ended and the channel is drained (shutdown, or
        // an unrecoverable acceptor exit). `Listener::accept` returns no
        // `Result` and axum loops on it, so we must neither panic nor busy-loop:
        // park here forever (awaiting the shutdown token, then a never-resolving
        // future) so axum's own graceful-shutdown path drives teardown instead
        // of us spinning.
        self.shutdown.cancelled().await;
        std::future::pending().await
    }

    fn local_addr(&self) -> std::io::Result<Self::Addr> {
        Ok(self.local_addr)
    }
}

/// The outcome of inspecting a configured certificate + key pair, offline.
#[derive(Debug, Clone, Copy)]
pub struct LeafInspection {
    /// The leaf certificate's `notBefore`, as a UNIX timestamp (seconds).
    pub not_before_unix: i64,
    /// The leaf certificate's `notAfter`, as a UNIX timestamp (seconds).
    pub not_after_unix: i64,
}

impl LeafInspection {
    /// Whether the leaf certificate is not yet valid at `now_unix` — its
    /// `notBefore` lies in the future. Such a certificate fails every handshake
    /// until its validity window opens, so the runtime rejects it at startup and
    /// doctor grades it a failure, symmetric to [`Self::is_expired`].
    #[must_use]
    pub const fn is_not_yet_valid(&self, now_unix: i64) -> bool {
        now_unix < self.not_before_unix
    }

    /// Whole days from `now_unix` until `notAfter`. Negative once expired.
    ///
    /// Note: this truncates toward zero, so a certificate that expired less
    /// than 24h ago still reports `0` days. Callers grading expiry must use
    /// [`Self::is_expired`] for the pass/fail decision rather than relying on
    /// this day bucket.
    #[must_use]
    pub const fn days_until_expiry(&self, now_unix: i64) -> i64 {
        (self.not_after_unix - now_unix) / 86_400
    }

    /// Whether the leaf certificate has already expired at `now_unix`.
    ///
    /// Decided from the raw `notAfter` timestamp (not the truncated day
    /// bucket), so a certificate expired even seconds ago reports `true` —
    /// matching the runtime, which rejects such a pair at startup.
    #[must_use]
    pub const fn is_expired(&self, now_unix: i64) -> bool {
        self.not_after_unix <= now_unix
    }
}

/// Validate the configured certificate + key and report the leaf's expiry,
/// WITHOUT booting a server or touching the network. Used by `autumn doctor`.
///
/// This performs the same parsing and cert/key-match validation as
/// [`load_certified_key`] (so a broken pair is reported), but tolerates a LEAF
/// outside its validity window — already-expired OR not-yet-valid — leaving the
/// caller to decide how to grade it, by still returning the `notBefore`/
/// `notAfter` bounds. Non-leaf (intermediate) certificates are NOT tolerated:
/// an expired or not-yet-valid intermediate is rejected here (mirroring the
/// runtime), since clients reject the served chain during path validation.
///
/// `now_unix` is the current UNIX time; it is a parameter (rather than read
/// internally) so tests can pin "now" deterministically. It is used only to
/// lifetime-check the intermediates — the leaf's window is returned ungraded.
///
/// # Errors
///
/// Returns a [`TlsError`] for a missing/unreadable file, unparseable PEM, an
/// empty certificate file, a key that does not match the leaf certificate, or a
/// malformed / expired / not-yet-valid intermediate certificate.
pub fn inspect_leaf(
    cert_path: &Path,
    key_path: &Path,
    now_unix: i64,
) -> Result<LeafInspection, TlsError> {
    let chain = read_cert_chain(cert_path)?;
    let key = read_private_key(key_path)?;
    let (not_before, not_after) = leaf_validity_unix(cert_path, &chain[0])?;

    // Parse and lifetime-check every intermediate too, so doctor fails a
    // malformed — or expired / not-yet-valid — intermediate chain instead of
    // greenlighting one the runtime would boot but clients reject (rustls
    // validates only the leaf).
    validate_chain_certs(cert_path, &chain, now_unix)?;

    // Validate the key matches the leaf even though we do not need the key
    // material — a mismatched pair would fail every handshake at runtime, so
    // doctor should surface it too.
    let provider = crypto_provider();
    CertifiedKey::from_der(chain, key, &provider).map_err(|source| TlsError::InvalidKeyPair {
        cert: cert_path.to_path_buf(),
        key: key_path.to_path_buf(),
        source: Box::new(source),
    })?;

    Ok(LeafInspection {
        not_before_unix: not_before,
        not_after_unix: not_after,
    })
}

/// Build a rustls [`CertifiedKey`] from an in-memory PEM certificate chain and
/// private key, WITHOUT touching the filesystem.
///
/// Used by the ACME path (issue #1608) to hot-swap a freshly issued certificate
/// into a [`ReloadableCertResolver`] without a round-trip through disk, and by
/// the custom-domain SNI cache (issue #1635) to parse a per-tenant certificate
/// read back from the store. Like
/// [`load_certified_key`], `from_der` validates the key and checks it matches
/// the leaf; unlike it, this does not reject an expired leaf (the caller — the
/// renewal task — decides how to react to a stale cert, and the self-signed
/// placeholder it also loads is deliberately short-lived).
///
/// # Errors
///
/// Returns a human-readable message if the PEM cannot be parsed or the key does
/// not match the leaf certificate.
pub fn certified_key_from_pem(
    chain_pem: &[u8],
    key_pem: &[u8],
    provider: &CryptoProvider,
) -> Result<Arc<CertifiedKey>, String> {
    let mut chain = Vec::new();
    for cert in CertificateDer::pem_slice_iter(chain_pem) {
        chain.push(cert.map_err(|e| format!("failed to parse ACME certificate PEM: {e}"))?);
    }
    if chain.is_empty() {
        return Err("ACME certificate chain contained no PEM CERTIFICATE blocks".to_owned());
    }
    let key = PrivateKeyDer::from_pem_slice(key_pem)
        .map_err(|e| format!("failed to parse ACME private key PEM: {e}"))?;
    let certified = CertifiedKey::from_der(chain, key, provider)
        .map_err(|e| format!("ACME private key does not match the issued certificate: {e}"))?;
    Ok(Arc::new(certified))
}

/// The leaf certificate's `notAfter` (UNIX seconds) from an in-memory PEM chain.
///
/// Used by the ACME renewal loop and health indicator — and by the per-domain
/// custom-domain renewal scheduler (#1635) — to decide when a stored
/// certificate is due for renewal. Returns an error message if the PEM has no
/// certificate or the leaf cannot be parsed.
///
/// # Errors
///
/// Returns a human-readable message on a missing or unparseable leaf.
pub fn leaf_not_after_from_pem(chain_pem: &[u8]) -> Result<i64, String> {
    let leaf = CertificateDer::pem_slice_iter(chain_pem)
        .next()
        .ok_or_else(|| "certificate chain contained no PEM CERTIFICATE blocks".to_owned())?
        .map_err(|e| format!("failed to parse certificate PEM: {e}"))?;
    leaf_validity_unix(Path::new("<memory>"), &leaf)
        .map(|(_, not_after)| not_after)
        .map_err(|e| e.to_string())
}

/// Wall-clock seconds since the epoch — the reference instant certificate
/// validity is judged against, and the one deliberate real-time read in this
/// module.
///
/// Deliberately **real** time, not the injected clock: a certificate's
/// `notBefore`/`notAfter` are facts about the real world, so a test or
/// simulation clock pinned to the sim epoch must never be able to declare a
/// live certificate not-yet-valid (or an expired one fine).
#[allow(
    clippy::disallowed_methods,
    reason = "TLS certificate validity is judged against real wall time by \
              design — see this function's doc comment. Injecting a virtual \
              clock here would let a simulation misjudge a real certificate."
)]
pub(crate) fn now_unix() -> i64 {
    std::time::SystemTime::now()
        .duration_since(std::time::UNIX_EPOCH)
        .map_or(0, |d| i64::try_from(d.as_secs()).unwrap_or(i64::MAX))
}

/// Modification times of the cert and key files, `None` for a file that could
/// not be stat'd. Reloads trigger on any change to this pair.
fn file_mtimes(
    cert: &Path,
    key: &Path,
) -> (Option<std::time::SystemTime>, Option<std::time::SystemTime>) {
    let mtime = |p: &Path| std::fs::metadata(p).and_then(|m| m.modified()).ok();
    (mtime(cert), mtime(key))
}

/// The background certificate hot-reloader (issue #1603).
///
/// Polls the cert/key file mtimes and swaps the served certificate in place
/// when either changes, so a `certbot` / ACME renewal is picked up **without a
/// restart and without dropping the site**.
///
/// Never breaks the listener: a failed reload logs an error, keeps the
/// previously loaded certificate, and retries on the next tick. The baseline
/// mtimes only advance on a *successful* load, so a partial write observed
/// mid-renewal is retried rather than skipped.
///
/// `app.rs` constructs one of these when `[server.tls]` names a static cert and
/// spawns [`run`](Self::run) as a child of the server's shutdown token.
pub struct CertReloader {
    resolver: Arc<ReloadableCertResolver>,
    provider: Arc<CryptoProvider>,
    cert_path: PathBuf,
    key_path: PathBuf,
    interval: std::time::Duration,
    /// Mtimes of the cert/key as of just *before* the load whose certificate
    /// the resolver serves (see [`load`](Self::load)). Captured there rather
    /// than on the loop's first tick so a renewal landing anywhere between the
    /// load and the first poll is still seen as a change.
    baseline: (Option<std::time::SystemTime>, Option<std::time::SystemTime>),
}

impl CertReloader {
    /// Load the certificate and key, build the resolver that will serve them,
    /// and build the reloader that watches them — deliberately one operation,
    /// in that order.
    ///
    /// The baseline mtimes are stat'd **before** the load. Any other ordering
    /// loses a renewal: stat after loading and a renewal that lands in the gap
    /// is recorded as the baseline while the resolver still holds the
    /// superseded certificate, so every later poll sees "no change" and the old
    /// certificate is served until the *next* renewal. Stat-first can only ever
    /// cost a redundant reload of a certificate already in hand.
    ///
    /// `interval` is the mtime poll period (see
    /// [`DEFAULT_RELOAD_INTERVAL_SECS`]). A zero interval would busy-loop, so
    /// [`run`](Self::run) substitutes the default for it rather than spinning.
    ///
    /// # Errors
    ///
    /// Returns the same [`TlsError`] as
    /// [`load_certified_key`](crate::tls::load_certified_key): a missing or
    /// unreadable file, unparseable or empty PEM, a key that does not match the
    /// leaf, or an expired / not-yet-valid certificate in the chain.
    pub fn load(
        cert_path: PathBuf,
        key_path: PathBuf,
        provider: Arc<CryptoProvider>,
        now_unix_secs: i64,
        interval: std::time::Duration,
    ) -> Result<(Arc<ReloadableCertResolver>, Self), TlsError> {
        let baseline = file_mtimes(&cert_path, &key_path);
        let certified = load_certified_key(&cert_path, &key_path, &provider, now_unix_secs)?;
        let resolver = Arc::new(ReloadableCertResolver::new(certified));
        let reloader = Self {
            resolver: Arc::clone(&resolver),
            provider,
            cert_path,
            key_path,
            interval,
            baseline,
        };
        Ok((resolver, reloader))
    }

    /// Run the poll loop until `shutdown` is cancelled.
    pub async fn run(self, shutdown: tokio_util::sync::CancellationToken) {
        // A zero interval would spin the loop (and its two `spawn_blocking`
        // stats per tick) as fast as the runtime allows. `app.rs` clamps
        // `reload_interval_secs` before constructing this, but the type is
        // public, so enforce the invariant where it belongs instead of trusting
        // every caller to know it.
        let interval = if self.interval.is_zero() {
            std::time::Duration::from_secs(DEFAULT_RELOAD_INTERVAL_SECS)
        } else {
            self.interval
        };
        // Stat and PEM-read the cert/key on a blocking thread — both touch the
        // filesystem and must not run on a tokio worker. On a `JoinError` (the
        // blocking pool shutting down) just skip the tick and retry next time.
        let stat_mtimes = |cert: PathBuf, key: PathBuf| {
            crate::time::spawn_blocking(move || file_mtimes(&cert, &key))
        };

        // The baseline was taken when the served certificate was loaded, so a
        // renewal between then and the first tick below is a change, not the
        // status quo.
        let mut last = self.baseline;
        loop {
            tokio::select! {
                () = tokio::time::sleep(interval) => {}
                () = shutdown.cancelled() => break,
            }

            let current = match stat_mtimes(self.cert_path.clone(), self.key_path.clone()).await {
                Ok(mtimes) => mtimes,
                Err(e) => {
                    tracing::warn!(error = %e, "TLS reload: mtime read task failed; skipping tick");
                    continue;
                }
            };
            if current == last {
                continue;
            }

            let cert_path = self.cert_path.clone();
            let key_path = self.key_path.clone();
            let provider = Arc::clone(&self.provider);
            let loaded = crate::time::spawn_blocking(move || {
                load_certified_key(&cert_path, &key_path, &provider, now_unix())
            })
            .await;
            let loaded = match loaded {
                Ok(result) => result,
                Err(e) => {
                    tracing::warn!(error = %e, "TLS reload: load task failed; skipping tick");
                    continue;
                }
            };

            match loaded {
                Ok(next) => {
                    self.resolver.store(next);
                    // Only advance the baseline on a successful load, so a
                    // partial write observed mid-renewal is retried on the
                    // next tick.
                    last = current;
                    tracing::info!(
                        cert = %self.cert_path.display(),
                        "Reloaded TLS certificate after detecting a change on disk"
                    );
                }
                Err(e) => {
                    tracing::error!(
                        error = %e,
                        cert = %self.cert_path.display(),
                        "TLS certificate reload failed; keeping the previously loaded certificate"
                    );
                }
            }
        }
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use std::io::Write as _;

    // Self-signed `CN=localhost`, valid until 2126. Test fixture only — the key
    // pair is intentionally public (mirrors `tests/integration/pg_tls.rs`).
    const CERT_PEM: &str = include_str!("../tests/fixtures/tls/localhost.cert.pem");
    const KEY_PEM: &str = include_str!("../tests/fixtures/tls/localhost.key.pem");
    // A second, unrelated self-signed key (does not match `CERT_PEM`).
    const MISMATCHED_KEY_PEM: &str = include_str!("../tests/fixtures/tls/other.key.pem");
    // Self-signed `CN=localhost` that expired in 2021.
    const EXPIRED_CERT_PEM: &str = include_str!("../tests/fixtures/tls/expired.cert.pem");
    const EXPIRED_KEY_PEM: &str = include_str!("../tests/fixtures/tls/expired.key.pem");

    // A well-formed PEM CERTIFICATE block whose body is valid base64 but NOT a
    // parseable X.509 DER (all-zero bytes). PEM-decodes fine, so it survives
    // `read_cert_chain`, but `X509Certificate::from_der` rejects it — standing in
    // for a malformed intermediate in a chain.
    const MALFORMED_CERT_PEM: &str = "\
-----BEGIN CERTIFICATE-----
AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
-----END CERTIFICATE-----
";

    fn write_temp(dir: &Path, name: &str, contents: &str) -> PathBuf {
        let path = dir.join(name);
        let mut f = std::fs::File::create(&path).unwrap();
        f.write_all(contents.as_bytes()).unwrap();
        path
    }

    fn now() -> i64 {
        std::time::SystemTime::now()
            .duration_since(std::time::UNIX_EPOCH)
            .unwrap()
            .as_secs()
            .try_into()
            .unwrap()
    }

    #[test]
    fn load_valid_pair_succeeds() {
        let dir = tempfile::tempdir().unwrap();
        let cert = write_temp(dir.path(), "c.pem", CERT_PEM);
        let key = write_temp(dir.path(), "k.pem", KEY_PEM);
        let provider = crypto_provider();
        let ck = load_certified_key(&cert, &key, &provider, now()).expect("valid pair loads");
        assert!(!ck.cert.is_empty());
    }

    // Regression (#1603, Codex): rustls validates only the leaf, so a malformed
    // INTERMEDIATE would boot a listener serving a chain normal clients reject.
    // `load_certified_key` must parse every cert in the chain and fail fast,
    // naming the offending 1-based position.
    #[test]
    fn malformed_intermediate_in_chain_is_rejected() {
        let dir = tempfile::tempdir().unwrap();
        // [valid leaf, malformed intermediate].
        let chain_pem = format!("{CERT_PEM}\n{MALFORMED_CERT_PEM}");
        let cert = write_temp(dir.path(), "chain.pem", &chain_pem);
        let key = write_temp(dir.path(), "k.pem", KEY_PEM);
        let provider = crypto_provider();
        let err = load_certified_key(&cert, &key, &provider, now()).unwrap_err();
        assert!(
            matches!(err, TlsError::ParseChainCert { position: 2, .. }),
            "a malformed intermediate must fail fast naming its chain position, got {err:?}"
        );
        assert!(
            err.to_string().contains("#2"),
            "error must name the offending position, got: {err}"
        );
    }

    // A chain of [valid leaf, well-formed valid intermediate] still loads.
    // Chain-cert validation checks DER parseability and the validity window
    // (not chain-of-trust), so a second currently-valid certificate stands in
    // for a real intermediate here.
    #[test]
    fn valid_leaf_and_intermediate_chain_loads() {
        let dir = tempfile::tempdir().unwrap();
        // Both blocks are the far-future `CERT_PEM` fixture, so the intermediate
        // is within its validity window (an expired intermediate is now rejected).
        let chain_pem = format!("{CERT_PEM}\n{CERT_PEM}");
        let cert = write_temp(dir.path(), "chain.pem", &chain_pem);
        let key = write_temp(dir.path(), "k.pem", KEY_PEM);
        let provider = crypto_provider();
        let ck = load_certified_key(&cert, &key, &provider, now())
            .expect("a valid leaf + well-formed intermediate must load");
        assert_eq!(ck.cert.len(), 2, "both chain certificates are retained");
    }

    // Regression (#1603, Codex): an EXPIRED intermediate is rejected by clients
    // during path validation, so `validate_chain_certs` must fail fast at
    // load/inspection time, naming the 1-based position and that it expired.
    #[test]
    fn expired_intermediate_in_chain_is_rejected() {
        let dir = tempfile::tempdir().unwrap();
        // [valid leaf (far-future), expired intermediate (2021)].
        let chain_pem = format!("{CERT_PEM}\n{EXPIRED_CERT_PEM}");
        let path = write_temp(dir.path(), "chain.pem", &chain_pem);
        let chain = read_cert_chain(&path).unwrap();
        // "Now" is inside the leaf's window but well past the intermediate's
        // 2021 notAfter.
        let err = validate_chain_certs(&path, &chain, now()).unwrap_err();
        assert!(
            matches!(err, TlsError::ExpiredChainCert { position: 2, .. }),
            "an expired intermediate must fail fast at position 2, got {err:?}"
        );
        assert!(
            err.to_string().contains("#2"),
            "error must name the offending position, got: {err}"
        );
        assert!(
            err.to_string().contains("expired"),
            "error must report expiry, got: {err}"
        );
    }

    // Regression (#1603, Codex): a NOT-YET-VALID intermediate is likewise
    // rejected by clients, so it must fail fast at position 2. `now` is pinned
    // before the intermediate's notBefore; the leaf (`chain[0]`) is skipped by
    // `validate_chain_certs`, so only the intermediate is graded.
    #[test]
    fn not_yet_valid_intermediate_in_chain_is_rejected() {
        let dir = tempfile::tempdir().unwrap();
        let leaf = write_temp(dir.path(), "leaf.pem", CERT_PEM);
        let leaf_key = write_temp(dir.path(), "leaf.key.pem", KEY_PEM);
        // The intermediate is a second copy of `CERT_PEM`; pin "now" one hour
        // before its notBefore so its validity window has not opened yet.
        let not_before = inspect_leaf(&leaf, &leaf_key, now())
            .unwrap()
            .not_before_unix;
        let chain_pem = format!("{CERT_PEM}\n{CERT_PEM}");
        let path = write_temp(dir.path(), "chain.pem", &chain_pem);
        let chain = read_cert_chain(&path).unwrap();
        let err = validate_chain_certs(&path, &chain, not_before - 3600).unwrap_err();
        assert!(
            matches!(err, TlsError::NotYetValidChainCert { position: 2, .. }),
            "a not-yet-valid intermediate must fail fast at position 2, got {err:?}"
        );
        assert!(
            err.to_string().contains("#2"),
            "error must name the offending position, got: {err}"
        );
        assert!(
            err.to_string().contains("not yet valid"),
            "error must report the not-yet-valid window, got: {err}"
        );
    }

    // A chain whose intermediate is currently within its validity window passes.
    #[test]
    fn valid_intermediate_in_chain_is_accepted() {
        let dir = tempfile::tempdir().unwrap();
        let chain_pem = format!("{CERT_PEM}\n{CERT_PEM}");
        let path = write_temp(dir.path(), "chain.pem", &chain_pem);
        let chain = read_cert_chain(&path).unwrap();
        validate_chain_certs(&path, &chain, now())
            .expect("a valid, in-window intermediate must be accepted");
    }

    #[test]
    fn missing_cert_file_names_the_path() {
        let dir = tempfile::tempdir().unwrap();
        let key = write_temp(dir.path(), "k.pem", KEY_PEM);
        let missing = dir.path().join("does-not-exist.pem");
        let provider = crypto_provider();
        let err = load_certified_key(&missing, &key, &provider, now()).unwrap_err();
        assert!(matches!(err, TlsError::ReadCert { .. }));
        assert!(err.to_string().contains("does-not-exist.pem"));
    }

    #[test]
    fn unparseable_cert_pem_is_reported() {
        let dir = tempfile::tempdir().unwrap();
        let cert = write_temp(dir.path(), "c.pem", "not a pem file");
        let key = write_temp(dir.path(), "k.pem", KEY_PEM);
        let provider = crypto_provider();
        let err = load_certified_key(&cert, &key, &provider, now()).unwrap_err();
        // An input with no PEM blocks yields "no certificates"; a malformed
        // block yields a parse error. Either is an actionable, path-named error.
        assert!(matches!(
            err,
            TlsError::NoCertificates { .. } | TlsError::ParseCert { .. }
        ));
    }

    #[test]
    fn mismatched_key_is_rejected() {
        let dir = tempfile::tempdir().unwrap();
        let cert = write_temp(dir.path(), "c.pem", CERT_PEM);
        let key = write_temp(dir.path(), "k.pem", MISMATCHED_KEY_PEM);
        let provider = crypto_provider();
        let err = load_certified_key(&cert, &key, &provider, now()).unwrap_err();
        assert!(
            matches!(err, TlsError::InvalidKeyPair { .. }),
            "got {err:?}"
        );
    }

    #[test]
    fn expired_leaf_is_rejected() {
        let dir = tempfile::tempdir().unwrap();
        let cert = write_temp(dir.path(), "c.pem", EXPIRED_CERT_PEM);
        let key = write_temp(dir.path(), "k.pem", EXPIRED_KEY_PEM);
        let provider = crypto_provider();
        let err = load_certified_key(&cert, &key, &provider, now()).unwrap_err();
        assert!(matches!(err, TlsError::Expired { .. }), "got {err:?}");
    }

    #[test]
    fn not_yet_valid_leaf_is_rejected() {
        let dir = tempfile::tempdir().unwrap();
        let cert = write_temp(dir.path(), "c.pem", CERT_PEM);
        let key = write_temp(dir.path(), "k.pem", KEY_PEM);
        let provider = crypto_provider();

        // Pin "now" to one hour BEFORE the fixture's notBefore (equivalent to a
        // cert whose notBefore is now + 3600): the leaf is not yet valid, so
        // load must fail fast — symmetric to the expired-leaf rejection.
        let not_before = inspect_leaf(&cert, &key, now()).unwrap().not_before_unix;
        let err = load_certified_key(&cert, &key, &provider, not_before - 3600).unwrap_err();
        assert!(matches!(err, TlsError::NotYetValid { .. }), "got {err:?}");

        // A currently-valid cert is unaffected: one second into the validity
        // window (and well before notAfter) the same pair loads cleanly.
        load_certified_key(&cert, &key, &provider, not_before + 1)
            .expect("cert loads once notBefore has passed");
    }

    #[test]
    fn inspect_reports_not_yet_valid_window() {
        let dir = tempfile::tempdir().unwrap();
        let cert = write_temp(dir.path(), "c.pem", CERT_PEM);
        let key = write_temp(dir.path(), "k.pem", KEY_PEM);
        // inspect_leaf tolerates a not-yet-valid leaf (doctor grades it) but
        // returns notBefore so the caller can see the window has not opened.
        let inspection = inspect_leaf(&cert, &key, now()).expect("pair inspects");
        assert!(inspection.is_not_yet_valid(inspection.not_before_unix - 1));
        assert!(!inspection.is_not_yet_valid(inspection.not_before_unix));
        assert!(!inspection.is_not_yet_valid(inspection.not_after_unix));
    }

    #[test]
    fn inspect_reports_future_expiry() {
        let dir = tempfile::tempdir().unwrap();
        let cert = write_temp(dir.path(), "c.pem", CERT_PEM);
        let key = write_temp(dir.path(), "k.pem", KEY_PEM);
        let inspection = inspect_leaf(&cert, &key, now()).expect("valid pair inspects");
        assert!(
            inspection.days_until_expiry(now()) > 30,
            "fixture should be valid far into the future"
        );
    }

    #[test]
    fn inspect_still_reports_expiry_for_expired_cert() {
        let dir = tempfile::tempdir().unwrap();
        let cert = write_temp(dir.path(), "c.pem", EXPIRED_CERT_PEM);
        let key = write_temp(dir.path(), "k.pem", EXPIRED_KEY_PEM);
        // inspect_leaf tolerates expiry (doctor grades it) but still returns
        // the notAfter so the caller can see it is in the past.
        let inspection = inspect_leaf(&cert, &key, now()).expect("expired pair still inspects");
        assert!(inspection.days_until_expiry(now()) < 0);
    }

    #[test]
    fn reloadable_resolver_swaps_certificate() {
        let dir = tempfile::tempdir().unwrap();
        let cert = write_temp(dir.path(), "c.pem", CERT_PEM);
        let key = write_temp(dir.path(), "k.pem", KEY_PEM);
        let provider = crypto_provider();
        let first = load_certified_key(&cert, &key, &provider, now()).unwrap();
        let resolver = ReloadableCertResolver::new(Arc::clone(&first));
        assert!(Arc::ptr_eq(&resolver.current(), &first));

        let second = load_certified_key(&cert, &key, &provider, now()).unwrap();
        resolver.store(Arc::clone(&second));
        assert!(Arc::ptr_eq(&resolver.current(), &second));
    }

    // Regression (#2321): `build_server_config` never set `alpn_protocols`,
    // so rustls completed the handshake with no protocol selected and every
    // browser silently fell back to HTTP/1.1 — even though the serve path's
    // `hyper_util::server::conn::auto` already speaks h2 once the client
    // sends the preface. The fix advertises `h2` first, then `http/1.1`:
    // ALPN-less and http/1.1-only clients are unaffected.
    #[tokio::test(flavor = "multi_thread")]
    async fn no_connection_is_accepted_before_the_cap_is_installed() {
        let dir = tempfile::tempdir().unwrap();
        let cert = write_temp(dir.path(), "c.pem", CERT_PEM);
        let key = write_temp(dir.path(), "k.pem", KEY_PEM);
        let provider = crypto_provider();
        let certified = load_certified_key(&cert, &key, &provider, now()).unwrap();
        let config =
            build_server_config(provider, Arc::new(ReloadableCertResolver::new(certified)))
                .unwrap();
        let tcp = tokio::net::TcpListener::bind("127.0.0.1:0").await.unwrap();
        let addr = tcp.local_addr().unwrap();
        let shutdown = tokio_util::sync::CancellationToken::new();
        let mut listener = TlsListener::new(
            tcp,
            config,
            std::time::Duration::from_secs(30),
            shutdown.clone(),
        );
        // Two silent clients wait in the kernel backlog before the serve arm
        // installs the cap (for example during an upgrade's startup hooks).
        let _first = tokio::net::TcpStream::connect(addr).await.unwrap();
        let _second = tokio::net::TcpStream::connect(addr).await.unwrap();
        tokio::time::sleep(std::time::Duration::from_millis(300)).await;
        assert_eq!(listener.handshakes_in_flight(), 0, "nothing starts early");
        assert!(listener.limit_connections(1).is_some());
        tokio::time::sleep(std::time::Duration::from_millis(300)).await;
        // Installing the cap does not start the acceptor: an upgrade successor
        // installs it before its startup hooks run, and must not take
        // connections from its predecessor until the server is polled.
        assert_eq!(
            listener.handshakes_in_flight(),
            0,
            "the cap alone starts nothing"
        );
        let handshakes = Arc::clone(&listener.handshakes);
        let serving = tokio::spawn(async move {
            let _ = axum::serve::Listener::accept(&mut listener).await;
        });
        tokio::time::sleep(std::time::Duration::from_millis(300)).await;
        assert_eq!(
            MAX_CONCURRENT_HANDSHAKES - handshakes.available_permits(),
            1,
            "with max_connections = 1, the second client waits before its handshake"
        );
        shutdown.cancel();
        serving.abort();
    }

    #[tokio::test(flavor = "multi_thread")]
    async fn the_public_serve_caps_tls_connections_before_the_handshake() {
        let dir = tempfile::tempdir().unwrap();
        let cert = write_temp(dir.path(), "c.pem", CERT_PEM);
        let key = write_temp(dir.path(), "k.pem", KEY_PEM);
        let provider = crypto_provider();
        let certified = load_certified_key(&cert, &key, &provider, now()).unwrap();
        let config =
            build_server_config(provider, Arc::new(ReloadableCertResolver::new(certified)))
                .unwrap();
        let tcp = tokio::net::TcpListener::bind("127.0.0.1:0").await.unwrap();
        let addr = tcp.local_addr().unwrap();
        let shutdown = tokio_util::sync::CancellationToken::new();
        let listener = TlsListener::new(
            tcp,
            config,
            std::time::Duration::from_secs(30),
            shutdown.clone(),
        );
        let handshakes = Arc::clone(&listener.handshakes);
        let limits = crate::http_server::HttpLimits {
            max_connections: Some(1),
            ..crate::http_server::HttpLimits::default()
        };
        let signal = shutdown.clone();
        tokio::spawn(crate::http_server::serve(
            listener,
            axum::Router::new().into_make_service(),
            limits,
            async move { signal.cancelled().await },
        ));
        // Two clients that never send a ClientHello.
        let _first = tokio::net::TcpStream::connect(addr).await.unwrap();
        let _second = tokio::net::TcpStream::connect(addr).await.unwrap();
        tokio::time::sleep(std::time::Duration::from_millis(300)).await;
        assert_eq!(
            MAX_CONCURRENT_HANDSHAKES - handshakes.available_permits(),
            1,
            "with max_connections = 1, the public serve must not start a second handshake"
        );
        shutdown.cancel();
    }

    #[tokio::test]
    async fn the_connection_cap_applies_before_the_tls_handshake() {
        let dir = tempfile::tempdir().unwrap();
        let cert = write_temp(dir.path(), "c.pem", CERT_PEM);
        let key = write_temp(dir.path(), "k.pem", KEY_PEM);
        let provider = crypto_provider();
        let certified = load_certified_key(&cert, &key, &provider, now()).unwrap();
        let config =
            build_server_config(provider, Arc::new(ReloadableCertResolver::new(certified)))
                .unwrap();
        let tcp = tokio::net::TcpListener::bind("127.0.0.1:0").await.unwrap();
        let addr = tcp.local_addr().unwrap();
        let handshakes = Arc::new(tokio::sync::Semaphore::new(MAX_CONCURRENT_HANDSHAKES));
        let cap = Some(Arc::new(tokio::sync::Semaphore::new(1)));
        let (tx, _rx) = tokio::sync::mpsc::channel(READY_CONN_CHANNEL_CAPACITY);
        let shutdown = tokio_util::sync::CancellationToken::new();
        tokio::spawn(run_acceptor(
            tcp,
            tokio_rustls::TlsAcceptor::from(config),
            std::time::Duration::from_secs(30),
            Arc::clone(&handshakes),
            cap,
            tx,
            shutdown.clone(),
        ));
        // Two clients that never send a ClientHello.
        let _first = tokio::net::TcpStream::connect(addr).await.unwrap();
        let _second = tokio::net::TcpStream::connect(addr).await.unwrap();
        tokio::time::sleep(std::time::Duration::from_millis(300)).await;
        assert_eq!(
            MAX_CONCURRENT_HANDSHAKES - handshakes.available_permits(),
            1,
            "with max_connections = 1, the second client waits before its handshake"
        );
        shutdown.cancel();
    }

    #[test]
    fn server_config_advertises_h2_then_http11_alpn() {
        let dir = tempfile::tempdir().unwrap();
        let cert = write_temp(dir.path(), "c.pem", CERT_PEM);
        let key = write_temp(dir.path(), "k.pem", KEY_PEM);
        let provider = crypto_provider();
        let certified = load_certified_key(&cert, &key, &provider, now()).unwrap();
        let config =
            build_server_config(provider, Arc::new(ReloadableCertResolver::new(certified)))
                .expect("server config builds");
        assert_eq!(
            config.alpn_protocols,
            vec![b"h2".to_vec(), b"http/1.1".to_vec()],
            "the static [server.tls] path must advertise h2 first, then http/1.1"
        );
    }

    // The ACME path (#1608) funnels through `build_server_config_with_resolver`
    // and the client-auth path (#1640) takes a different `match` arm, so pin
    // the ALPN on both entry points rather than assuming the shared funnel.
    #[test]
    fn server_config_with_resolver_and_client_auth_advertise_the_same_alpn() {
        let dir = tempfile::tempdir().unwrap();
        let cert = write_temp(dir.path(), "c.pem", CERT_PEM);
        let key = write_temp(dir.path(), "k.pem", KEY_PEM);
        let provider = crypto_provider();
        let certified = load_certified_key(&cert, &key, &provider, now()).unwrap();
        let expected = vec![b"h2".to_vec(), b"http/1.1".to_vec()];

        let via_resolver = build_server_config_with_resolver(
            Arc::clone(&provider),
            Arc::new(ReloadableCertResolver::new(Arc::clone(&certified)))
                as Arc<dyn ResolvesServerCert>,
        )
        .expect("resolver config builds");
        assert_eq!(
            via_resolver.alpn_protocols, expected,
            "the resolver (ACME) entry point must advertise the same ALPN"
        );

        // rustls refuses to build a client verifier with zero trust anchors
        // (`NoRootAnchors`) even in `Optional` mode, so load the client CA
        // fixture instead of an empty store — the anchors are irrelevant to
        // the ALPN assertion below; only the `Some(verifier)` arm matters.
        let ca = write_temp(
            dir.path(),
            "ca.pem",
            include_str!("../tests/fixtures/tls/client/ca.cert.pem"),
        );
        let verifier = client_auth::build_client_verifier(
            client_auth::load_client_roots(&ca).expect("client roots load"),
            vec![],
            crate::config::ClientAuthMode::Optional,
            Arc::clone(&provider),
        )
        .expect("client verifier builds");
        let via_client_auth = build_server_config_with_client_auth(
            provider,
            Arc::new(ReloadableCertResolver::new(certified)) as Arc<dyn ResolvesServerCert>,
            Some(verifier),
        )
        .expect("client-auth config builds");
        assert_eq!(
            via_client_auth.alpn_protocols, expected,
            "the client-auth arm must advertise the same ALPN"
        );
    }

    // Regression (Codex P1 on PR #2780): advertising `h2` in ALPN is only
    // safe while the serve stack can speak HTTP/2. The serve loop
    // (`crate::http_server`) runs every connection through
    // `hyper_util::server::conn::auto::Builder`, whose H2 arm is compiled out
    // unless hyper-util's `http2` feature is on. `Builder::http2()` exists
    // only under that feature, so this test does not compile without it.
    #[test]
    fn serve_stack_speaks_http2() {
        let mut builder =
            hyper_util::server::conn::auto::Builder::new(hyper_util::rt::TokioExecutor::new());
        let _ = builder.http2();
    }
}