broadcast_auth/

server.rs

//! Server-side challenge + verify — the origin half of RFC 7235
//! (`WWW-Authenticate`/`Authorization`), RFC 7617 (Basic), RFC 7616 (Digest),
//! RFC 2326 §14 (RTSP's reuse of the same two schemes), and RFC 6750
//! (Bearer).
//!
//! [`crate::Authenticator`]/[`crate::respond`] are the *client* half: answer
//! a challenge. [`Verifier`] is the other side of the same handshake: an
//! origin (multimux's shared output auth gating every `/{stream}/…` route,
//! issue #663; or any other credentialed origin in this workspace) builds
//! one from a configured [`Credentials`] + realm, calls [`Verifier::challenge`]
//! for the `WWW-Authenticate` value to send on a `401`, and
//! [`Verifier::verify`] to check an incoming `Authorization` header.
//!
//! Promoted from `multimux`'s test-only mock auth server
//! (`multimux::testutil`, issue #663 "Finish client-side multi-scheme
//! auth"): that module's Digest verification was already a real,
//! independent RFC 7616 §3.4.1 computation (not a literal-string match)
//! purely to drive multimux's own client-side tests against something that
//! genuinely rejects wrong credentials. This module is that same
//! computation, promoted into the shared crate so it is the *production*
//! server-side verifier (multimux's output-auth middleware) rather than a
//! test-only fixture, and so no crate hand-rolls a second copy.
//!
//! # Verification per scheme
//!
//! - **Basic** (RFC 7617 §2): the header's base64 payload is decoded and
//!   compared, in constant time, against `"{username}:{password}"`.
//! - **Bearer** (RFC 6750 §2.1): the token is compared, in constant time,
//!   against the configured token.
//! - **Digest** (RFC 7616 §3.4.1): `HA1 = MD5(username:realm:password)`,
//!   `HA2 = MD5(method:uri)`, `response = MD5(HA1:nonce:nc:cnonce:qop:HA2)`
//!   — `qop=auth`/`algorithm=MD5` only (the one shape every client in this
//!   workspace answers) — recomputed and compared, in constant time, against
//!   the client's `response` field. The client's claimed `uri` field must
//!   also match the actual request URI (RFC 7616 §3.4.1: the server "SHOULD
//!   check" this), not merely be internally consistent with its own
//!   `response`.
//! - **Forwarded** ([`Self::forwarded`], issue #663 extensibility wave part
//!   1): not an RFC 7235 challenge scheme at all — trusts that a fronting
//!   reverse proxy has already authenticated the caller and forwards the
//!   authenticated username in a configured header (conventionally
//!   `X-Forwarded-User`). Authenticated iff that header is present and
//!   non-empty. **Safe ONLY behind a trusted reverse proxy that strips any
//!   client-supplied copies of that header (and of the forwarded-for header,
//!   if configured) before forwarding** — this crate performs no such
//!   stripping and trusts [`crate::RequestContext::headers`] completely; a
//!   direct or spoofed client could otherwise set the header itself and
//!   bypass authentication entirely. [`Self::challenge`] returns just the
//!   bare scheme name for diagnostics (there is no challenge/response
//!   round-trip a direct client could answer).
//!
//! # Nonce handling (replay caveat)
//!
//! A [`Verifier`] built for `Digest` generates one random nonce at
//! construction time and reuses it for the verifier's entire lifetime — it
//! does not rotate per-challenge or track consumed `(nonce, nc)` pairs. This
//! is the "simple server nonce" the design spec calls out as acceptable: it
//! is enough to stop a passive credential-sniffing attacker (the password
//! itself is never sent), but — unlike a nonce-tracking implementation — it
//! does **not** detect a replayed exact request (identical `nc`/`cnonce`)
//! within the verifier's lifetime. Rebuild the `Verifier` (e.g. on process
//! restart) to rotate the nonce.

use base64::Engine;
use md5::{Digest as _, Md5};

use crate::credentials::Credentials;
use crate::request::RequestContext;

/// The outcome of [`Verifier::verify`].
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
#[non_exhaustive]
pub enum AuthResult {
    /// The `Authorization` header (or absence of one) satisfies the
    /// verifier's configured credential.
    Ok,
    /// Missing, malformed, or wrong-credential `Authorization` — the caller
    /// should respond `401` with [`Verifier::challenge`].
    Unauthorized,
}

/// Per-scheme state a [`Verifier`] holds — mirrors [`Credentials`] but adds
/// the realm (Basic/Digest) and the one server nonce (Digest) generated at
/// construction (see the module docs' nonce-handling caveat).
enum VerifierScheme {
    Basic {
        username: String,
        password: String,
        realm: String,
    },
    Digest {
        username: String,
        password: String,
        realm: String,
        nonce: String,
    },
    Bearer {
        token: String,
    },
    /// Reverse-proxy forwarded-auth (see the module docs) — no
    /// `Credentials`/realm/nonce at all, since there is no client-answered
    /// challenge for this scheme.
    Forwarded {
        user_header: String,
        forwarded_for_header: Option<String>,
    },
}

/// Challenges + verifies incoming requests against one configured
/// [`Credentials`] (RFC 7235 origin-side auth) — see the module docs.
pub struct Verifier {
    scheme: VerifierScheme,
}

impl Verifier {
    /// Builds a verifier for `credentials`, using `realm` for the
    /// `WWW-Authenticate` challenge (Basic/Digest only — RFC 6750 Bearer has
    /// no realm parameter in this crate's minimal challenge, see
    /// [`Self::challenge`]).
    ///
    /// For `Credentials::Digest`, a fresh random server nonce is generated
    /// now and held for this verifier's whole lifetime (see the module
    /// docs' nonce-handling caveat).
    pub fn new(credentials: Credentials, realm: impl Into<String>) -> Self {
        let realm = realm.into();
        let scheme = match credentials {
            Credentials::Basic { username, password } => VerifierScheme::Basic {
                username,
                password,
                realm,
            },
            Credentials::Digest { username, password } => VerifierScheme::Digest {
                username,
                password,
                realm,
                nonce: generate_nonce(),
            },
            Credentials::Bearer { token } => VerifierScheme::Bearer { token },
        };
        Verifier { scheme }
    }

    /// Builds a verifier for the reverse-proxy forwarded-auth scheme (see the
    /// module docs' trust assumption — read it before using this).
    ///
    /// `user_header` (conventionally `X-Forwarded-User`) is the header whose
    /// presence (non-empty) [`Self::verify`] treats as "the proxy already
    /// authenticated this caller". `forwarded_for_header` (conventionally
    /// `Some("X-Forwarded-For".to_string())`), if configured, is read back by
    /// [`Self::forwarded_for`] for observability only — this crate makes no
    /// trust decision based on it.
    pub fn forwarded(user_header: impl Into<String>, forwarded_for_header: Option<String>) -> Self {
        Verifier {
            scheme: VerifierScheme::Forwarded {
                user_header: user_header.into(),
                forwarded_for_header,
            },
        }
    }

    /// The `WWW-Authenticate` header value to send on a `401` in response to
    /// a missing/failed [`Self::verify`] call.
    ///
    /// `Forwarded` (built via [`Self::forwarded`]) has no real RFC 7235
    /// challenge (a direct client cannot answer it — see the module docs);
    /// this just names the scheme for diagnostics.
    pub fn challenge(&self) -> String {
        match &self.scheme {
            VerifierScheme::Basic { realm, .. } => format!("Basic realm=\"{realm}\""),
            VerifierScheme::Digest { realm, nonce, .. } => {
                format!("Digest realm=\"{realm}\", nonce=\"{nonce}\", qop=\"auth\", algorithm=MD5")
            }
            VerifierScheme::Bearer { .. } => "Bearer".to_string(),
            VerifierScheme::Forwarded { .. } => "Forwarded".to_string(),
        }
    }

    /// Verifies an incoming request against this verifier's configured
    /// scheme.
    ///
    /// Basic/Digest/Bearer read `ctx`'s `Authorization` header
    /// ([`RequestContext::header`], case-insensitive) — missing entirely is
    /// `Unauthorized`, same as before this took a full [`RequestContext`].
    /// `ctx.method`/`ctx.uri` are needed for the Digest `HA2`/`uri`-match
    /// check (RFC 7616 §3.4.1); unused for Basic/Bearer. Forwarded reads
    /// `ctx`'s configured user header instead — see the module docs.
    ///
    /// A pathologically large `Digest` `Authorization` header is rejected
    /// outright rather than parsed (see `MAX_DIGEST_FIELDS`) — this bounds
    /// the per-request allocation cost, but is not a substitute for a
    /// transport-level cap on header size, which callers should also enforce.
    pub fn verify(&self, ctx: &RequestContext<'_>) -> AuthResult {
        let ok = match &self.scheme {
            VerifierScheme::Basic {
                username, password, ..
            } => ctx
                .header("authorization")
                .is_some_and(|header| verify_basic(header, username, password)),
            VerifierScheme::Bearer { token } => ctx
                .header("authorization")
                .is_some_and(|header| verify_bearer(header, token)),
            VerifierScheme::Digest {
                username,
                password,
                realm,
                nonce,
            } => ctx.header("authorization").is_some_and(|header| {
                verify_digest(
                    header, username, password, realm, nonce, ctx.method, ctx.uri,
                )
            }),
            VerifierScheme::Forwarded { user_header, .. } => verify_forwarded(ctx, user_header),
        };
        if ok {
            AuthResult::Ok
        } else {
            AuthResult::Unauthorized
        }
    }

    /// For a [`Self::forwarded`] verifier with a configured
    /// `forwarded_for_header`, returns that header's value from `ctx` — for
    /// tracing/observability only; this crate makes no trust decision with
    /// it (the module docs' trust assumption is what actually matters).
    /// `None` for any other verifier, or when no such header is
    /// configured/present in `ctx`.
    pub fn forwarded_for<'a>(&self, ctx: &RequestContext<'a>) -> Option<&'a str> {
        match &self.scheme {
            VerifierScheme::Forwarded {
                forwarded_for_header: Some(header_name),
                ..
            } => ctx.header(header_name),
            _ => None,
        }
    }
}

/// Manual `Debug` (rather than `#[derive(Debug)]`): every scheme carries a
/// secret (`password`/`token`) that must never render verbatim.
impl core::fmt::Debug for Verifier {
    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
        let scheme = match &self.scheme {
            VerifierScheme::Basic { .. } => "Basic",
            VerifierScheme::Digest { .. } => "Digest",
            VerifierScheme::Bearer { .. } => "Bearer",
            VerifierScheme::Forwarded { .. } => "Forwarded",
        };
        f.debug_struct("Verifier")
            .field("scheme", &scheme)
            .finish_non_exhaustive()
    }
}

/// RFC 7617 §2: decode the base64 payload and compare, in constant time,
/// against `"{username}:{password}"`.
fn verify_basic(header: &str, username: &str, password: &str) -> bool {
    let Some(encoded) = header.strip_prefix("Basic ") else {
        return false;
    };
    let Ok(decoded) = base64::engine::general_purpose::STANDARD.decode(encoded.trim()) else {
        return false;
    };
    let expected = format!("{username}:{password}");
    constant_time_eq(&decoded, expected.as_bytes())
}

/// RFC 6750 §2.1: compare the bearer token, in constant time.
fn verify_bearer(header: &str, token: &str) -> bool {
    let Some(sent) = header.strip_prefix("Bearer ") else {
        return false;
    };
    constant_time_eq(sent.trim().as_bytes(), token.as_bytes())
}

/// A real Digest `Authorization` response (RFC 7616 §3.4.1) carries under 15
/// `key=value` fields (`username`, `realm`, `nonce`, `uri`, `response`,
/// `algorithm`, `cnonce`, `opaque`, `qop`, `nc`, plus a couple of optional
/// extensions). Capping well above that bounds [`verify_digest`]'s
/// `HashMap` allocation against a request carrying a pathologically large
/// `Authorization` header (a huge field count forcing a huge per-request
/// map) without rejecting any legitimate client.
const MAX_DIGEST_FIELDS: usize = 64;

/// RFC 7616 §3.4.1: parse the `Digest` `Authorization` header's
/// `key=value`/`key="value"` fields, independently recompute the expected
/// `response`, and compare in constant time — `qop=auth`/`algorithm=MD5`
/// only (the one shape every client in this workspace answers).
///
/// Also checks the client's claimed `uri` field against the actual request
/// `uri` (RFC 7616 §3.4.1's SHOULD) rather than only using whatever the
/// client claims to compute `HA2`.
///
/// Rejects outright (without building the field map) a header carrying more
/// than [`MAX_DIGEST_FIELDS`] comma-separated fields — see that constant's
/// docs.
fn verify_digest(
    header: &str,
    username: &str,
    password: &str,
    realm: &str,
    nonce: &str,
    method: &str,
    uri: &str,
) -> bool {
    let Some(rest) = header.strip_prefix("Digest ") else {
        return false;
    };
    if rest.split(',').count() > MAX_DIGEST_FIELDS {
        return false;
    }
    let mut fields = std::collections::HashMap::new();
    for part in rest.split(',') {
        let part = part.trim();
        let Some((key, value)) = part.split_once('=') else {
            continue;
        };
        fields.insert(key.trim(), value.trim().trim_matches('"'));
    }
    let get = |k: &str| fields.get(k).copied().unwrap_or_default();

    if get("username") != username || get("realm") != realm || get("nonce") != nonce {
        return false;
    }
    if get("uri") != uri {
        return false;
    }
    let nc = get("nc");
    let cnonce = get("cnonce");
    let qop = get("qop");
    let client_response = get("response");
    if nc.is_empty() || cnonce.is_empty() || client_response.is_empty() {
        return false;
    }

    let ha1 = md5_hex(format!("{username}:{realm}:{password}"));
    let ha2 = md5_hex(format!("{method}:{uri}"));
    let expected_response = md5_hex(format!("{ha1}:{nonce}:{nc}:{cnonce}:{qop}:{ha2}"));
    constant_time_eq(expected_response.as_bytes(), client_response.as_bytes())
}

/// Reverse-proxy forwarded-auth (see the module docs): authenticated iff
/// `user_header` is present in `ctx` and non-empty (after trimming) — the
/// proxy having already verified the caller's identity. No credential/secret
/// is compared here, so no constant-time comparison is needed.
fn verify_forwarded(ctx: &RequestContext<'_>, user_header: &str) -> bool {
    ctx.header(user_header)
        .is_some_and(|v| !v.trim().is_empty())
}

/// Lowercase-hex MD5 digest of `input`.
fn md5_hex(input: String) -> String {
    let mut hasher = Md5::new();
    hasher.update(input.as_bytes());
    let digest = hasher.finalize();
    digest.iter().map(|b| format!("{b:02x}")).collect()
}

/// Byte-equality that does not short-circuit on the first differing byte —
/// only the *length* check short-circuits (an equal-length requirement is
/// not itself the secret being protected). Guards against a timing
/// side-channel on the password/token/digest-response comparison.
fn constant_time_eq(a: &[u8], b: &[u8]) -> bool {
    if a.len() != b.len() {
        return false;
    }
    a.iter()
        .zip(b.iter())
        .fold(0u8, |acc, (x, y)| acc | (x ^ y))
        == 0
}

/// A fresh 128-bit random server nonce, lowercase-hex encoded — see the
/// module docs' nonce-handling caveat.
fn generate_nonce() -> String {
    let bytes: [u8; 16] = rand::random();
    bytes.iter().map(|b| format!("{b:02x}")).collect()
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::{Credentials, RequestContext, respond};

    const REALM: &str = "cameras";

    /// Test helper: builds a [`RequestContext`] carrying `authorization` (if
    /// any) as the `Authorization` header, then verifies it — stands in for
    /// the pre-#663-extensibility-wave-1 `Verifier::verify(Option<&str>,
    /// &str, &str)` signature so the tests below read the same as before.
    fn verify_auth(
        v: &Verifier,
        authorization: Option<&str>,
        method: &str,
        uri: &str,
    ) -> AuthResult {
        let auth_header = authorization.map(|h| [("authorization", h)]);
        let headers: &[(&str, &str)] = match &auth_header {
            Some(arr) => arr,
            None => &[],
        };
        let ctx = RequestContext::new(method, uri).with_headers(headers);
        v.verify(&ctx)
    }

    // --- challenge() shape ---

    #[test]
    fn basic_challenge_names_the_realm() {
        let v = Verifier::new(
            Credentials::Basic {
                username: "admin".into(),
                password: "12345".into(),
            },
            REALM,
        );
        assert_eq!(v.challenge(), "Basic realm=\"cameras\"");
    }

    #[test]
    fn digest_challenge_carries_realm_nonce_qop_algorithm() {
        let v = Verifier::new(
            Credentials::Digest {
                username: "admin".into(),
                password: "12345".into(),
            },
            REALM,
        );
        let challenge = v.challenge();
        assert!(challenge.starts_with("Digest "), "got: {challenge}");
        for needle in [
            "realm=\"cameras\"",
            "nonce=",
            "qop=\"auth\"",
            "algorithm=MD5",
        ] {
            assert!(
                challenge.contains(needle),
                "missing {needle} in {challenge}"
            );
        }
    }

    #[test]
    fn bearer_challenge_is_bare_scheme_name() {
        let v = Verifier::new(Credentials::bearer("tok"), REALM);
        assert_eq!(v.challenge(), "Bearer");
    }

    #[test]
    fn digest_nonce_is_stable_across_repeated_challenge_calls() {
        let v = Verifier::new(
            Credentials::Digest {
                username: "admin".into(),
                password: "12345".into(),
            },
            REALM,
        );
        assert_eq!(
            v.challenge(),
            v.challenge(),
            "nonce must not rotate per-call"
        );
    }

    // --- round trip: a client's respond() to challenge() must verify() Ok ---

    #[test]
    fn basic_respond_to_challenge_verifies_ok() {
        let v = Verifier::new(
            Credentials::Basic {
                username: "admin".into(),
                password: "12345".into(),
            },
            REALM,
        );
        let header = respond(
            &v.challenge(),
            &RequestContext::new("GET", "/stream"),
            Credentials::new("admin", "12345"),
        )
        .unwrap();
        assert_eq!(
            verify_auth(&v, Some(&header), "GET", "/stream"),
            AuthResult::Ok
        );
    }

    #[test]
    fn digest_respond_to_challenge_verifies_ok() {
        let v = Verifier::new(
            Credentials::Digest {
                username: "admin".into(),
                password: "12345".into(),
            },
            REALM,
        );
        let ctx = RequestContext::new("DESCRIBE", "rtsp://cam/live");
        let header = respond(&v.challenge(), &ctx, Credentials::new("admin", "12345")).unwrap();
        assert_eq!(
            verify_auth(&v, Some(&header), "DESCRIBE", "rtsp://cam/live"),
            AuthResult::Ok
        );
    }

    #[test]
    fn bearer_respond_to_challenge_verifies_ok() {
        let v = Verifier::new(Credentials::bearer("mytoken123"), REALM);
        let header = respond(
            &v.challenge(),
            &RequestContext::new("GET", "/stream"),
            Credentials::bearer("mytoken123"),
        )
        .unwrap();
        assert_eq!(
            verify_auth(&v, Some(&header), "GET", "/stream"),
            AuthResult::Ok
        );
    }

    // --- wrong credentials -> Unauthorized (must BITE) ---

    #[test]
    fn basic_wrong_password_is_unauthorized() {
        let v = Verifier::new(
            Credentials::Basic {
                username: "admin".into(),
                password: "12345".into(),
            },
            REALM,
        );
        let header = respond(
            &v.challenge(),
            &RequestContext::new("GET", "/stream"),
            Credentials::new("admin", "WRONG"),
        )
        .unwrap();
        assert_eq!(
            verify_auth(&v, Some(&header), "GET", "/stream"),
            AuthResult::Unauthorized
        );
    }

    #[test]
    fn digest_wrong_password_is_unauthorized() {
        let v = Verifier::new(
            Credentials::Digest {
                username: "admin".into(),
                password: "12345".into(),
            },
            REALM,
        );
        let ctx = RequestContext::new("DESCRIBE", "rtsp://cam/live");
        let header = respond(&v.challenge(), &ctx, Credentials::new("admin", "WRONG")).unwrap();
        assert_eq!(
            verify_auth(&v, Some(&header), "DESCRIBE", "rtsp://cam/live"),
            AuthResult::Unauthorized
        );
    }

    #[test]
    fn digest_mismatched_request_uri_is_unauthorized() {
        // A digest response computed for one URI must not verify against a
        // different URI the caller passes to `verify` (RFC 7616 SHOULD-check
        // that the header's `uri` matches the actual request).
        let v = Verifier::new(
            Credentials::Digest {
                username: "admin".into(),
                password: "12345".into(),
            },
            REALM,
        );
        let ctx = RequestContext::new("DESCRIBE", "rtsp://cam/live");
        let header = respond(&v.challenge(), &ctx, Credentials::new("admin", "12345")).unwrap();
        assert_eq!(
            verify_auth(&v, Some(&header), "DESCRIBE", "rtsp://cam/OTHER"),
            AuthResult::Unauthorized
        );
    }

    #[test]
    fn bearer_wrong_token_is_unauthorized() {
        let v = Verifier::new(Credentials::bearer("right-token"), REALM);
        let header = respond(
            &v.challenge(),
            &RequestContext::new("GET", "/stream"),
            Credentials::bearer("wrong-token"),
        )
        .unwrap();
        assert_eq!(
            verify_auth(&v, Some(&header), "GET", "/stream"),
            AuthResult::Unauthorized
        );
    }

    #[test]
    fn missing_authorization_header_is_unauthorized() {
        let v = Verifier::new(Credentials::bearer("tok"), REALM);
        assert_eq!(
            verify_auth(&v, None, "GET", "/stream"),
            AuthResult::Unauthorized
        );
    }

    #[test]
    fn wrong_scheme_header_is_unauthorized() {
        // A Basic-configured verifier must reject a Bearer-shaped header
        // (and vice versa) rather than mis-parsing it as a match.
        let v = Verifier::new(
            Credentials::Basic {
                username: "admin".into(),
                password: "12345".into(),
            },
            REALM,
        );
        assert_eq!(
            verify_auth(&v, Some("Bearer sometoken"), "GET", "/stream"),
            AuthResult::Unauthorized
        );
    }

    // --- Forwarded (reverse-proxy forwarded-auth, issue #663 extensibility
    // wave part 1) ---

    #[test]
    fn forwarded_challenge_is_bare_scheme_name() {
        let v = Verifier::forwarded("X-Forwarded-User", Some("X-Forwarded-For".to_string()));
        assert_eq!(v.challenge(), "Forwarded");
    }

    /// Biting test: a request carrying the configured user header (non-empty)
    /// must verify `Ok` — this is the whole trust mechanism, no secret is
    /// ever compared.
    #[test]
    fn forwarded_with_user_header_present_is_ok() {
        let v = Verifier::forwarded("X-Forwarded-User", Some("X-Forwarded-For".to_string()));
        let headers: &[(&str, &str)] = &[("X-Forwarded-User", "alice")];
        let ctx = RequestContext::new("GET", "/stream").with_headers(headers);
        assert_eq!(v.verify(&ctx), AuthResult::Ok);
    }

    /// Biting test: a request with no user header at all must `Unauthorized`
    /// — the whole point of the scheme is that only a trusted proxy having
    /// authenticated the caller sets it.
    #[test]
    fn forwarded_without_user_header_is_unauthorized() {
        let v = Verifier::forwarded("X-Forwarded-User", Some("X-Forwarded-For".to_string()));
        let ctx = RequestContext::new("GET", "/stream");
        assert_eq!(v.verify(&ctx), AuthResult::Unauthorized);
    }

    /// An empty (but present) user header must not count as authenticated —
    /// otherwise a proxy bug forwarding an empty header would silently grant
    /// access.
    #[test]
    fn forwarded_with_empty_user_header_is_unauthorized() {
        let v = Verifier::forwarded("X-Forwarded-User", Some("X-Forwarded-For".to_string()));
        let headers: &[(&str, &str)] = &[("X-Forwarded-User", "")];
        let ctx = RequestContext::new("GET", "/stream").with_headers(headers);
        assert_eq!(v.verify(&ctx), AuthResult::Unauthorized);
    }

    /// The user-header lookup is case-insensitive, matching real HTTP header
    /// semantics (RFC 7230 §3.2) rather than a literal-string match.
    #[test]
    fn forwarded_user_header_lookup_is_case_insensitive() {
        let v = Verifier::forwarded("X-Forwarded-User", None);
        let headers: &[(&str, &str)] = &[("x-forwarded-user", "alice")];
        let ctx = RequestContext::new("GET", "/stream").with_headers(headers);
        assert_eq!(v.verify(&ctx), AuthResult::Ok);
    }

    /// Biting test: `forwarded_for` reads the configured header's value back
    /// out of the request context — the mechanism the origin middleware uses
    /// to surface the proxy-forwarded client IP to tracing.
    #[test]
    fn forwarded_for_reads_configured_header() {
        let v = Verifier::forwarded("X-Forwarded-User", Some("X-Forwarded-For".to_string()));
        let headers: &[(&str, &str)] = &[
            ("X-Forwarded-User", "alice"),
            ("X-Forwarded-For", "203.0.113.7"),
        ];
        let ctx = RequestContext::new("GET", "/stream").with_headers(headers);
        assert_eq!(v.forwarded_for(&ctx), Some("203.0.113.7"));
    }

    /// With no `forwarded_for_header` configured, `forwarded_for` is always
    /// `None`, even if an `X-Forwarded-For` header happens to be present.
    #[test]
    fn forwarded_for_is_none_when_not_configured() {
        let v = Verifier::forwarded("X-Forwarded-User", None);
        let headers: &[(&str, &str)] = &[("X-Forwarded-For", "203.0.113.7")];
        let ctx = RequestContext::new("GET", "/stream").with_headers(headers);
        assert_eq!(v.forwarded_for(&ctx), None);
    }

    /// `forwarded_for` is always `None` for a non-`Forwarded` verifier, even
    /// if the request happens to carry an `X-Forwarded-For` header.
    #[test]
    fn forwarded_for_is_none_for_non_forwarded_verifier() {
        let v = Verifier::new(Credentials::bearer("tok"), REALM);
        let headers: &[(&str, &str)] = &[("X-Forwarded-For", "203.0.113.7")];
        let ctx = RequestContext::new("GET", "/stream").with_headers(headers);
        assert_eq!(v.forwarded_for(&ctx), None);
    }

    /// Debug must never need to redact anything for `Forwarded` (no secret is
    /// involved), but must still not panic and must name the scheme.
    #[test]
    fn forwarded_debug_names_scheme() {
        let v = Verifier::forwarded("X-Forwarded-User", Some("X-Forwarded-For".to_string()));
        let debug = format!("{v:?}");
        assert!(debug.contains("Forwarded"), "debug: {debug}");
    }

    #[test]
    fn constant_time_eq_matches_naive_equality() {
        assert!(constant_time_eq(b"same", b"same"));
        assert!(!constant_time_eq(b"same", b"diff"));
        assert!(!constant_time_eq(b"short", b"longer-string"));
        assert!(constant_time_eq(b"", b""));
    }

    // Regression: an oversized Digest `Authorization` header (way more
    // `key=value` fields than any real client sends) must be rejected
    // outright rather than parsed into an unbounded `HashMap` — and must
    // never panic. Must FAIL if the `MAX_DIGEST_FIELDS` cap in
    // `verify_digest` is ever removed.
    #[test]
    fn oversized_digest_header_is_rejected_not_parsed() {
        let v = Verifier::new(
            Credentials::Digest {
                username: "admin".into(),
                password: "12345".into(),
            },
            REALM,
        );
        let mut huge = String::from("Digest ");
        for i in 0..(MAX_DIGEST_FIELDS + 1) {
            if i > 0 {
                huge.push(',');
            }
            huge.push_str(&format!("k{i}=\"v{i}\""));
        }
        assert_eq!(
            verify_auth(&v, Some(&huge), "DESCRIBE", "rtsp://cam/live"),
            AuthResult::Unauthorized,
            "oversized Digest header must not be accepted"
        );
    }

    #[test]
    fn debug_never_leaks_password_or_token() {
        let v = Verifier::new(
            Credentials::Digest {
                username: "admin".into(),
                password: "supersecret".into(),
            },
            REALM,
        );
        let debug = format!("{v:?}");
        assert!(!debug.contains("supersecret"), "debug: {debug}");

        let v = Verifier::new(Credentials::bearer("topsecrettoken"), REALM);
        let debug = format!("{v:?}");
        assert!(!debug.contains("topsecrettoken"), "debug: {debug}");
    }
}