fn0_deploy/

cloudflare_provision.rs

//! Provisioning a user's Cloudflare account, on the user's own machine.
//!
//! This is the half of bring-your-own-Cloudflare that deliberately does not run
//! on fn0's servers. Creating buckets, attaching a CDN hostname, writing a cache
//! rule, pointing the app hostname at the fleet and signing origin certificates
//! all need an account-wide token, and a token that can do those things can also
//! delete every bucket in the account.
//! Measured, not assumed: an account-scoped `Workers R2 Storage Edit` token
//! reaches every bucket in the account over the S3 API, `DeleteBucket`
//! included.
//!
//! So the account-wide token stays here and is discarded when the command
//! exits. What fn0 receives is what this module mints at the end: two R2 tokens
//! that cannot delete a bucket or call the REST API, and a token that can purge
//! one zone's cache and nothing else.
//!
//! The two R2 tokens are split by who holds them. The worker token reaches the
//! project's objects and public objects, and is the only one
//! published to the fleet; the asset token reaches the deployed frontend and
//! stays in control. So a compromised worker cannot rewrite a deployed
//! frontend, and asset GC — which is the only thing that deletes on a schedule
//! — holds a credential that cannot open a bucket holding user data.
//!
//! There are two ways in, because the convenient one asks for a permission not
//! everyone should grant.
//!
//! [`Provisioner::run_managed`] takes a setup token carrying only
//! `User -> API Tokens -> Edit` and mints everything else from it, including
//! the short-lived token that does the provisioning. Cloudflare lets a token
//! grant permissions it does not hold, so one checkbox is enough; it also
//! refuses to let a minted token mint further tokens, so the provisioning token
//! cannot widen itself. Both measured against the live API. The catch is that a
//! token which can create tokens can create *any* token, so it is account-wide
//! however short its list looks.
//!
//! [`Provisioner::run_manual`] takes a token that can provision but cannot
//! create tokens, and mints nothing. The user makes the two long-lived
//! credentials themselves. It is more work and it never puts a token capable of
//! escalation on disk.

use anyhow::{Context, Result, anyhow};
use serde::{Deserialize, Serialize};
use sha2::{Digest, Sha256};
use std::collections::BTreeSet;

const API_BASE: &str = "https://api.cloudflare.com/client/v4";

// Permission group ids, read from `/user/tokens/permission_groups`. Cloudflare
// identifies these by uuid rather than by name in the tokens API.
const R2_BUCKET_ITEM_READ: &str = "6a018a9f2fc74eb6b293b0c548f38b39";
const R2_BUCKET_ITEM_WRITE: &str = "2efd5506f9c8494dacb1fa10a3e7d5b6";
const CACHE_PURGE: &str = "e17beae8b8cb423a99b1730f21238bed";

/// Origin CA's longest offered validity. Renewal would be a live-traffic event
/// on a hostname fn0 does not control the DNS for, so the fewer the better.
const CERTIFICATE_VALIDITY_DAYS: u32 = 5475;
const SECONDS_PER_DAY: i64 = 86_400;

/// rcgen generates an ECDSA P-256 key by default, which Origin CA signs under
/// `origin-ecc`. Asking for `origin-rsa` with an ECDSA CSR is rejected.
const CERTIFICATE_REQUEST_TYPE: &str = "origin-ecc";

// Permission groups the provisioning token is minted with. Setup is seconds of
// API calls; the expiry is generous by comparison and exists so that a crash
// between minting and revoking leaves nothing usable for long.
const PROVISIONING_TOKEN_MINUTES: i64 = 10;
const R2_STORAGE_WRITE: &str = "bf7481a1826f439697cb59a20b22293e";
const ZONE_READ: &str = "c8fed203ed3043cba015a93ad1616f1f";
/// `DNS Write`, not `Zone DNS Settings Write`: the latter carries the zone's DNS
/// settings and cannot touch a record.
const DNS_WRITE: &str = "4755a26eedb94da69e1066d98aa820be";
const CACHE_SETTINGS_WRITE: &str = "9ff81cbbe65c400b97d92c3c1033cab6";
const ZONE_SETTINGS_WRITE: &str = "3030687196b94b638145a3953da2b699";
const SSL_AND_CERTIFICATES_WRITE: &str = "c03055bc037c4ea9afb9a9f104b7b721";

/// One set of buckets per project. The two that are served publicly take their
/// hostname from their own name, so a bucket and the address it answers on are
/// the same string and cannot drift apart.
pub fn private_object_storage_bucket_name(project_id: &str) -> String {
    format!("fn0-{project_id}-private-object-storage")
}

pub fn public_object_storage_bucket_name(project_id: &str) -> String {
    format!("fn0-{project_id}-public-object-storage")
}

pub fn frontend_asset_bucket_name(project_id: &str) -> String {
    format!("fn0-{project_id}-frontend-asset")
}

/// A zone the setup token can reach, and the account that owns it.
pub struct ReachableZone {
    pub zone_id: String,
    pub zone_name: String,
    pub account_id: String,
    pub account_name: String,
}

/// Reads which zones a token can reach, so nobody has to copy a hex id out of
/// the dashboard. Separate from [`Provisioner`], which cannot be built until an
/// account and a zone have been picked — which is what this is for.
pub struct ZoneDiscovery {
    client: reqwest::Client,
    setup_token: String,
}

impl ZoneDiscovery {
    pub fn new(setup_token: String) -> Self {
        Self {
            client: reqwest::Client::new(),
            setup_token,
        }
    }

    /// `GET /zones` carries the owning account on every zone, so one call
    /// settles both ids.
    ///
    /// A setup token carries only `API Tokens -> Edit` and cannot read zones,
    /// so `mint_reader` has it mint one that can and revokes it afterwards. The
    /// minted policy scopes `com.cloudflare.api.account.*` — a wildcard the
    /// tokens API accepts, and the only form available here, since the account
    /// id is the thing being discovered. Measured against the live API.
    pub async fn list(&self, mint_reader: bool) -> Result<Vec<ReachableZone>> {
        if !mint_reader {
            return self.zones(&self.setup_token).await;
        }
        let expires_on = (chrono::Utc::now()
            + chrono::Duration::minutes(PROVISIONING_TOKEN_MINUTES))
        .format("%Y-%m-%dT%H:%M:%SZ")
        .to_string();
        let reader = mint_token(
            &self.client,
            &self.setup_token,
            "fn0 setup (zone discovery)",
            vec![serde_json::json!({
                "effect": "allow",
                "resources": { "com.cloudflare.api.account.*": "*" },
                "permission_groups": [{ "id": ZONE_READ }],
            })],
            Some(expires_on),
        )
        .await?;
        let result = self.zones(&reader.value).await;
        if let Err(error) = revoke_token(&self.client, &self.setup_token, &reader.id).await {
            eprintln!(
                "warning: could not revoke the zone discovery token: {error}. It expires by \
                 itself within {PROVISIONING_TOKEN_MINUTES} minutes."
            );
        }
        result
    }

    async fn zones(&self, token: &str) -> Result<Vec<ReachableZone>> {
        #[derive(Deserialize)]
        struct Zone {
            id: String,
            name: String,
            account: Account,
        }
        #[derive(Deserialize)]
        struct Account {
            id: String,
            #[serde(default)]
            name: String,
        }
        let (status, envelope) = call::<Vec<Zone>>(
            &self.client,
            token,
            reqwest::Method::GET,
            "/zones?per_page=200",
            None,
        )
        .await?;
        let zones = envelope.result.filter(|_| envelope.success).ok_or_else(|| {
            anyhow!(
                "could not list your zones ({status}). The token needs Zone -> Zone -> Read. {}",
                describe(&envelope.errors)
            )
        })?;
        Ok(zones
            .into_iter()
            .map(|zone| ReachableZone {
                zone_id: zone.id,
                zone_name: zone.name,
                account_id: zone.account.id,
                account_name: zone.account.name,
            })
            .collect())
    }
}

pub struct Provisioner {
    client: reqwest::Client,
    /// The user's setup token. Used only to mint and revoke; never to
    /// provision, because it is not granted the permissions to.
    setup_token: String,
    account_id: String,
    zone_id: String,
}

/// A token minted for the length of one command, and revoked at the end of it.
struct TemporaryToken {
    id: String,
    value: String,
}

/// What provisioning creates. Names only — no credentials.
pub struct ProvisionedResources {
    pub zone_name: String,
    pub frontend_asset_hostname: String,
    pub public_object_storage_hostname: String,
    pub private_object_storage_bucket: String,
    pub public_object_storage_bucket: String,
    pub frontend_asset_bucket: String,
}

/// The three long-lived credentials fn0 is given.
pub struct ConnectCredentials {
    /// Reaches the two object-storage buckets. The only R2 credential published
    /// to the worker fleet.
    pub worker_access_key_id: String,
    /// SHA-256 of the token, which is what R2 takes as an S3 secret access key.
    /// The token value never leaves the user's machine: the hash is the only
    /// form fn0 needs, and unlike the token it cannot be replayed against the
    /// REST API.
    pub worker_secret: String,
    /// Reaches the frontend-asset bucket only, and stays in control. Asset GC
    /// runs on a schedule and deletes; holding a credential that cannot open a
    /// bucket of user data is what keeps a bug in it from being unbounded.
    pub frontend_asset_access_key_id: String,
    pub frontend_asset_secret: String,
    pub purge_token: String,
}

/// The ids of the credentials the managed path minted, so a connect that fn0
/// refused does not leave them live on the user's account.
pub struct MintedCredentialIds {
    pub worker: String,
    pub frontend_asset: String,
    pub purge: String,
}

pub struct IssuedCertificate {
    pub certificate_pem: String,
    pub private_key_pem: String,
    pub not_after_epoch_seconds: i64,
}

#[derive(Deserialize)]
struct Envelope<T> {
    success: bool,
    #[serde(default)]
    errors: Vec<ApiError>,
    result: Option<T>,
}

#[derive(Deserialize)]
struct ApiError {
    #[serde(default)]
    code: i64,
    #[serde(default)]
    message: String,
}

async fn mint_token(
    client: &reqwest::Client,
    setup_token: &str,
    name: &str,
    policies: Vec<serde_json::Value>,
    expires_on: Option<String>,
) -> Result<TemporaryToken> {
    #[derive(Deserialize)]
    struct Minted {
        id: String,
        value: String,
    }
    let (status, envelope) = call::<Minted>(
        client,
        setup_token,
        reqwest::Method::POST,
        "/user/tokens",
        Some(match expires_on {
            Some(expires_on) => serde_json::json!({
                "name": name, "policies": policies, "expires_on": expires_on,
            }),
            None => serde_json::json!({ "name": name, "policies": policies }),
        }),
    )
    .await?;
    let minted = envelope.result.filter(|_| envelope.success).ok_or_else(|| {
        anyhow!(
            "could not mint the {name} token ({status}). The token needs User -> API Tokens -> Edit. {}",
            describe(&envelope.errors)
        )
    })?;
    Ok(TemporaryToken {
        id: minted.id,
        value: minted.value,
    })
}

async fn revoke_token(client: &reqwest::Client, setup_token: &str, id: &str) -> Result<()> {
    let (status, envelope) = call::<serde_json::Value>(
        client,
        setup_token,
        reqwest::Method::DELETE,
        &format!("/user/tokens/{id}"),
        None,
    )
    .await?;
    if envelope.success {
        return Ok(());
    }
    Err(anyhow!(
        "could not revoke token {id} ({status}): {}",
        describe(&envelope.errors)
    ))
}

async fn call<T: serde::de::DeserializeOwned>(
    client: &reqwest::Client,
    token: &str,
    method: reqwest::Method,
    path: &str,
    body: Option<serde_json::Value>,
) -> Result<(reqwest::StatusCode, Envelope<T>)> {
    let mut request = client
        .request(method, format!("{API_BASE}{path}"))
        .bearer_auth(token);
    if let Some(body) = body {
        request = request.json(&body);
    }
    let response = request.send().await?;
    let status = response.status();
    let text = response.text().await?;
    let envelope: Envelope<T> =
        serde_json::from_str(&text).with_context(|| format!("{path} returned {status}: {text}"))?;
    Ok((status, envelope))
}

fn describe(errors: &[ApiError]) -> String {
    if errors.is_empty() {
        return "no detail".to_string();
    }
    errors
        .iter()
        .map(|error| format!("{} ({})", error.message, error.code))
        .collect::<Vec<_>>()
        .join("; ")
}

impl Provisioner {
    pub fn new(setup_token: String, account_id: String, zone_id: String) -> Self {
        Self {
            client: reqwest::Client::new(),
            setup_token,
            account_id,
            zone_id,
        }
    }

    async fn call<T: serde::de::DeserializeOwned>(
        &self,
        token: &str,
        method: reqwest::Method,
        path: &str,
        body: Option<serde_json::Value>,
    ) -> Result<(reqwest::StatusCode, Envelope<T>)> {
        call(&self.client, token, method, path, body).await
    }

    /// Confirms the token works and returns its id, which is also the S3 access
    /// key id if this token is ever used against R2 directly.
    pub async fn verify(&self) -> Result<String> {
        #[derive(Deserialize)]
        struct Token {
            id: String,
            status: String,
        }
        // A token made under My Profile is user-owned; one made on the
        // account's own API Tokens page is account-owned, and each is only
        // accepted by its own endpoint. Onboarding documents the former.
        for path in [
            "/user/tokens/verify".to_string(),
            format!("/accounts/{}/tokens/verify", self.account_id),
        ] {
            if let Ok((_, envelope)) = self
                .call::<Token>(&self.setup_token, reqwest::Method::GET, &path, None)
                .await
                && let Some(token) = envelope.result.filter(|_| envelope.success)
            {
                if token.status != "active" {
                    return Err(anyhow!("the API token is {}, not active", token.status));
                }
                return Ok(token.id);
            }
        }
        Err(anyhow!(
            "Cloudflare rejected the API token. Check that it was copied whole and has not expired."
        ))
    }

    async fn zone_name(&self, token: &str) -> Result<String> {
        #[derive(Deserialize)]
        struct Zone {
            name: String,
        }
        let (_, envelope) = self
            .call::<Zone>(
                token,
                reqwest::Method::GET,
                &format!("/zones/{}", self.zone_id),
                None,
            )
            .await?;
        envelope
            .result
            .filter(|_| envelope.success)
            .map(|zone| zone.name)
            .ok_or_else(|| {
                anyhow!(
                    "could not read the zone. The token needs Zone -> Zone -> Read on it. {}",
                    describe(&envelope.errors)
                )
            })
    }

    async fn create_bucket(&self, token: &str, name: &str) -> Result<()> {
        let (status, envelope) = self
            .call::<serde_json::Value>(
                token,
                reqwest::Method::POST,
                &format!("/accounts/{}/r2/buckets", self.account_id),
                Some(serde_json::json!({ "name": name })),
            )
            .await?;
        if envelope.success || already_exists(&envelope.errors) {
            return Ok(());
        }
        Err(anyhow!(
            "could not create bucket {name} ({status}). The token needs Account -> Workers R2 Storage -> Edit. {}",
            describe(&envelope.errors)
        ))
    }

    /// Bounds who may read these objects from a browser to the one origin the
    /// project answers on. `None` removes the configuration entirely, which is
    /// how "no origin may read this" has to be spelled: R2 rejects both an
    /// empty `origins` and an empty `rules` with `10001`, measured against the
    /// live API.
    async fn put_cors(&self, token: &str, bucket: &str, app_origin: Option<&str>) -> Result<()> {
        let path = format!("/accounts/{}/r2/buckets/{bucket}/cors", self.account_id);
        let (method, body) = match app_origin {
            Some(origin) => (
                reqwest::Method::PUT,
                Some(serde_json::json!({
                    "rules": [{
                        "allowed": {
                            "methods": ["GET", "PUT", "HEAD"],
                            "origins": [origin],
                            "headers": ["*"],
                        },
                        "exposeHeaders": ["ETag"],
                        "maxAgeSeconds": 86400,
                    }],
                })),
            ),
            None => (reqwest::Method::DELETE, None),
        };
        let (status, envelope) = self
            .call::<serde_json::Value>(token, method, &path, body)
            .await?;
        // Deleting a configuration that was never written is the state asked
        // for, not a failure.
        if envelope.success || (app_origin.is_none() && cors_absent(&envelope.errors)) {
            return Ok(());
        }
        Err(anyhow!(
            "could not set CORS on {bucket} ({status}): {}",
            describe(&envelope.errors)
        ))
    }

    async fn attach_custom_domain(&self, token: &str, bucket: &str, hostname: &str) -> Result<()> {
        if self.custom_domain_present(token, bucket, hostname).await {
            return Ok(());
        }
        let (status, envelope) = self
            .call::<serde_json::Value>(
                token,
                reqwest::Method::POST,
                &format!(
                    "/accounts/{}/r2/buckets/{bucket}/domains/custom",
                    self.account_id
                ),
                Some(serde_json::json!({
                    "domain": hostname,
                    "zoneId": self.zone_id,
                    "enabled": true,
                })),
            )
            .await?;
        if envelope.success || already_exists(&envelope.errors) {
            return Ok(());
        }
        Err(anyhow!(
            "could not point {hostname} at {bucket} ({status}): {}",
            describe(&envelope.errors)
        ))
    }

    /// Whether `hostname` is already attached to `bucket` specifically.
    ///
    /// Cloudflare answers "already in use" for a hostname attached to any
    /// bucket, and [`already_exists`] deliberately refuses to read that as
    /// success — pointed at someone else's bucket it would serve 404s. Asking
    /// this bucket first is what makes a retry after a partial provision
    /// distinguishable from that.
    async fn custom_domain_present(&self, token: &str, bucket: &str, hostname: &str) -> bool {
        #[derive(Deserialize)]
        struct Domain {
            domain: String,
        }
        #[derive(Deserialize)]
        struct Domains {
            #[serde(default)]
            domains: Vec<Domain>,
        }

        let Ok((_, envelope)) = self
            .call::<Domains>(
                token,
                reqwest::Method::GET,
                &format!(
                    "/accounts/{}/r2/buckets/{bucket}/domains/custom",
                    self.account_id
                ),
                None,
            )
            .await
        else {
            return false;
        };
        envelope
            .result
            .filter(|_| envelope.success)
            .is_some_and(|listed| {
                listed
                    .domains
                    .iter()
                    .any(|attached| attached.domain == hostname)
            })
    }

    /// Adds the cache rule fn0's public hostnames need, keeping every other rule
    /// in the zone.
    ///
    /// The match is a wildcard over the whole zone rather than one hostname, so
    /// this rule is written once and never grows: a free zone allows ten cache
    /// rules, which a rule per project would exhaust at ten projects. Both
    /// halves of the pattern are required — a bare `*-frontend-asset` would also
    /// match a hostname of the user's own and quietly pull it into fn0's caching
    /// policy.
    ///
    /// A `PUT` to a phase entrypoint replaces the whole rule list, so the
    /// existing rules are read back and carried through. `PURGE` has to be in
    /// the method match or the purge API answers `success: true` while the edge
    /// keeps serving the old object. `browser_ttl: respect_origin` is what stops
    /// a fresh zone's four-hour default Browser Cache TTL from overriding the
    /// `max-age=0` fn0 stores on public objects — four hours of browser copies
    /// is the one staleness no purge can reach.
    async fn ensure_cache_rule(
        &self,
        token: &str,
        zone_name: &str,
        app_hostname: Option<&str>,
        replaced_app_hostname: Option<&str>,
    ) -> Result<()> {
        const RULE_DESCRIPTION: &str = "fn0 frontend assets and public objects";

        #[derive(Deserialize)]
        struct Ruleset {
            #[serde(default)]
            rules: Vec<serde_json::Value>,
        }

        let path = format!(
            "/zones/{}/rulesets/phases/http_request_cache_settings/entrypoint",
            self.zone_id
        );
        let (status, envelope) = self
            .call::<Ruleset>(token, reqwest::Method::GET, &path, None)
            .await?;
        // A zone with no cache rules has no entrypoint ruleset at all, which
        // reads as 404 rather than an empty list.
        let mut rules = if envelope.success {
            envelope.result.map(|set| set.rules).unwrap_or_default()
        } else if status == reqwest::StatusCode::NOT_FOUND {
            Vec::new()
        } else {
            return Err(anyhow!(
                "could not read the zone's cache rules ({status}). The token needs Zone -> Cache Rules -> Edit. {}",
                describe(&envelope.errors)
            ));
        };

        let managed_rule = rules.iter().find(|rule| {
            rule.get("description").and_then(|value| value.as_str()) == Some(RULE_DESCRIPTION)
        });
        let mut app_hostnames = managed_rule
            .map(cache_rule_app_hostnames)
            .unwrap_or_default();
        if let Some(replaced_app_hostname) = replaced_app_hostname {
            app_hostnames.remove(replaced_app_hostname);
        }
        if let Some(app_hostname) = app_hostname {
            app_hostnames.insert(app_hostname.to_string());
        }

        rules.retain(|rule| {
            rule.get("description").and_then(|value| value.as_str()) != Some(RULE_DESCRIPTION)
        });
        rules.insert(
            0,
            serde_json::json!({
                "action": "set_cache_settings",
                "expression": format!(
                    "(({}) and http.request.method in {{\"GET\" \"HEAD\" \"PURGE\"}})",
                    cache_rule_host_expression(zone_name, &app_hostnames),
                ),
                "description": RULE_DESCRIPTION,
                "action_parameters": {
                    "cache": true,
                    "browser_ttl": { "mode": "respect_origin" },
                },
            }),
        );

        let (status, envelope) = self
            .call::<serde_json::Value>(
                token,
                reqwest::Method::PUT,
                &path,
                Some(serde_json::json!({ "rules": rules })),
            )
            .await?;
        if envelope.success {
            return Ok(());
        }
        Err(anyhow!(
            "could not write the zone's cache rules ({status}). The token needs Zone -> Cache Rules -> Edit. {}",
            describe(&envelope.errors)
        ))
    }

    async fn ensure_tiered_cache(&self, token: &str) -> Result<()> {
        let path = format!(
            "/zones/{}/cache/tiered_cache_smart_topology_enable",
            self.zone_id
        );
        let (status, envelope) = self
            .call::<serde_json::Value>(
                token,
                reqwest::Method::PATCH,
                &path,
                Some(serde_json::json!({ "value": "on" })),
            )
            .await?;
        if envelope.success {
            return Ok(());
        }
        Err(anyhow!(
            "could not enable Smart Tiered Cache ({status}). The token needs Zone -> Zone Settings -> Edit. {}",
            describe(&envelope.errors)
        ))
    }

    pub async fn ensure_app_cache(
        &self,
        app_hostname: &str,
        replaced_app_hostname: Option<&str>,
        mint_writing_token: bool,
    ) -> Result<()> {
        if !mint_writing_token {
            let zone_name = self.zone_name(&self.setup_token).await?;
            self.ensure_tiered_cache(&self.setup_token).await?;
            return self
                .ensure_cache_rule(
                    &self.setup_token,
                    &zone_name,
                    Some(app_hostname),
                    replaced_app_hostname,
                )
                .await;
        }

        let writing = self.mint_provisioning_token(app_hostname).await?;
        let result = async {
            let zone_name = self.zone_name(&writing.value).await?;
            self.ensure_tiered_cache(&writing.value).await?;
            self.ensure_cache_rule(
                &writing.value,
                &zone_name,
                Some(app_hostname),
                replaced_app_hostname,
            )
            .await
        }
        .await;
        if let Err(error) = self.revoke_token("cache settings", &writing.id).await {
            eprintln!(
                "warning: {error}. It expires by itself within \
                 {PROVISIONING_TOKEN_MINUTES} minutes."
            );
        }
        result
    }

    /// Points the app hostname at the worker fleet and takes the record the
    /// project used to answer on back out of the zone.
    ///
    /// The record is proxied. An Origin CA certificate is trusted by
    /// Cloudflare's edge and by nothing else, so a grey-clouded record reaches
    /// the fleet and fails the handshake.
    ///
    /// Removing the replaced record is not tidying: it points at fn0 by name,
    /// and any project that registers that hostname next inherits the traffic.
    pub async fn ensure_app_dns_record(
        &self,
        app_hostname: &str,
        origin_hostname: &str,
        replaced_app_hostname: Option<&str>,
        mint_writing_token: bool,
    ) -> Result<()> {
        if !mint_writing_token {
            return self
                .write_app_dns_record(
                    &self.setup_token,
                    app_hostname,
                    origin_hostname,
                    replaced_app_hostname,
                )
                .await;
        }

        let writing = self.mint_provisioning_token(app_hostname).await?;
        let result = self
            .write_app_dns_record(
                &writing.value,
                app_hostname,
                origin_hostname,
                replaced_app_hostname,
            )
            .await;
        if let Err(error) = self.revoke_token("DNS record", &writing.id).await {
            eprintln!(
                "warning: {error}. It expires by itself within \
                 {PROVISIONING_TOKEN_MINUTES} minutes."
            );
        }
        result
    }

    async fn write_app_dns_record(
        &self,
        token: &str,
        app_hostname: &str,
        origin_hostname: &str,
        replaced_app_hostname: Option<&str>,
    ) -> Result<()> {
        let existing = self.dns_records(token, app_hostname).await?;
        match decide_app_dns_record(&existing, origin_hostname) {
            AppDnsRecordWrite::AlreadyPointed => {}
            AppDnsRecordWrite::Create => {
                self.create_app_dns_record(token, app_hostname, origin_hostname)
                    .await?
            }
            AppDnsRecordWrite::Repoint { record_id } => {
                self.repoint_app_dns_record(token, record_id, app_hostname, origin_hostname)
                    .await?
            }
            AppDnsRecordWrite::Occupied { record_types } => {
                return Err(anyhow!(
                    "{app_hostname} already resolves through {record_types} record(s), and only a \
                     CNAME can be repointed at {origin_hostname}. Delete them in the Cloudflare \
                     dashboard, or set the project up under a name that is free."
                ));
            }
        }

        // Guarded rather than assumed: control reports a replaced domain only
        // when it differs, and a version of it that ever reported the same one
        // would have this delete the record just written.
        if let Some(replaced_app_hostname) =
            replaced_app_hostname.filter(|replaced| *replaced != app_hostname)
        {
            self.remove_replaced_app_dns_record(token, replaced_app_hostname, origin_hostname)
                .await?;
        }
        Ok(())
    }

    /// Only the record this command itself would have written is removed.
    /// Anything else on that hostname is the user's, and a domain change is no
    /// reason to delete it for them.
    async fn remove_replaced_app_dns_record(
        &self,
        token: &str,
        replaced_app_hostname: &str,
        origin_hostname: &str,
    ) -> Result<()> {
        let zone_name = self.zone_name(token).await?;
        if !replaced_app_hostname.ends_with(&format!(".{zone_name}")) {
            eprintln!(
                "warning: {replaced_app_hostname} is not in {zone_name}, so its record still \
                 points at fn0. Delete it in the zone that holds it."
            );
            return Ok(());
        }

        let records = self.dns_records(token, replaced_app_hostname).await?;
        if records.is_empty() {
            return Ok(());
        }
        let Some(written_here) = replaced_app_dns_record(&records, origin_hostname) else {
            eprintln!(
                "warning: left the DNS record for {replaced_app_hostname} in place: it is not the \
                 proxied CNAME fn0 wrote. Read it, and remove it yourself if that hostname should \
                 stop resolving."
            );
            return Ok(());
        };
        self.delete_dns_record(token, &written_here.id, replaced_app_hostname)
            .await
    }

    /// `?name=` matches the whole name, measured against the live API: listing
    /// `example.com` answers with the apex records alone rather than everything
    /// under it.
    async fn dns_records(&self, token: &str, hostname: &str) -> Result<Vec<DnsRecord>> {
        let (status, envelope) = self
            .call::<Vec<DnsRecord>>(
                token,
                reqwest::Method::GET,
                &format!("/zones/{}/dns_records?name={hostname}", self.zone_id),
                None,
            )
            .await?;
        if envelope.success {
            return Ok(envelope.result.unwrap_or_default());
        }
        Err(anyhow!(
            "could not read the DNS records for {hostname} ({status}). The token needs Zone -> DNS -> Edit. {}",
            describe(&envelope.errors)
        ))
    }

    async fn create_app_dns_record(
        &self,
        token: &str,
        app_hostname: &str,
        origin_hostname: &str,
    ) -> Result<()> {
        let (status, envelope) = self
            .call::<serde_json::Value>(
                token,
                reqwest::Method::POST,
                &format!("/zones/{}/dns_records", self.zone_id),
                Some(serde_json::json!({
                    "type": "CNAME",
                    "name": app_hostname,
                    "content": origin_hostname,
                    "proxied": true,
                })),
            )
            .await?;
        if envelope.success {
            return Ok(());
        }
        Err(anyhow!(
            "could not point {app_hostname} at {origin_hostname} ({status}). The token needs Zone -> DNS -> Edit. {}",
            describe(&envelope.errors)
        ))
    }

    async fn repoint_app_dns_record(
        &self,
        token: &str,
        record_id: &str,
        app_hostname: &str,
        origin_hostname: &str,
    ) -> Result<()> {
        let (status, envelope) = self
            .call::<serde_json::Value>(
                token,
                reqwest::Method::PATCH,
                &format!("/zones/{}/dns_records/{record_id}", self.zone_id),
                Some(serde_json::json!({
                    "content": origin_hostname,
                    "proxied": true,
                })),
            )
            .await?;
        if envelope.success {
            return Ok(());
        }
        Err(anyhow!(
            "could not repoint {app_hostname} at {origin_hostname} ({status}). The token needs Zone -> DNS -> Edit. {}",
            describe(&envelope.errors)
        ))
    }

    async fn delete_dns_record(&self, token: &str, record_id: &str, hostname: &str) -> Result<()> {
        let (status, envelope) = self
            .call::<serde_json::Value>(
                token,
                reqwest::Method::DELETE,
                &format!("/zones/{}/dns_records/{record_id}", self.zone_id),
                None,
            )
            .await?;
        if envelope.success {
            return Ok(());
        }
        Err(anyhow!(
            "could not delete the DNS record for {hostname} ({status}). The token needs Zone -> DNS -> Edit. {}",
            describe(&envelope.errors)
        ))
    }

    async fn mint_with_expiry(
        &self,
        name: &str,
        policies: Vec<serde_json::Value>,
        expires_on: Option<String>,
    ) -> Result<(String, String)> {
        let minted =
            mint_token(&self.client, &self.setup_token, name, policies, expires_on).await?;
        Ok((minted.id, minted.value))
    }

    /// Mints a token that can do the provisioning, since the setup token
    /// itself is only allowed to create tokens.
    async fn mint_provisioning_token(&self, purpose: &str) -> Result<TemporaryToken> {
        let expires_on = (chrono::Utc::now()
            + chrono::Duration::minutes(PROVISIONING_TOKEN_MINUTES))
        .format("%Y-%m-%dT%H:%M:%SZ")
        .to_string();
        let (id, value) = self
            .mint_with_expiry(
                &format!("fn0 setup ({purpose})"),
                vec![
                    serde_json::json!({
                        "effect": "allow",
                        "resources": { format!("com.cloudflare.api.account.{}", self.account_id): "*" },
                        "permission_groups": [{ "id": R2_STORAGE_WRITE }],
                    }),
                    serde_json::json!({
                        "effect": "allow",
                        "resources": { format!("com.cloudflare.api.account.zone.{}", self.zone_id): "*" },
                        "permission_groups": [
                            { "id": ZONE_READ },
                            { "id": CACHE_SETTINGS_WRITE },
                            { "id": ZONE_SETTINGS_WRITE },
                            { "id": SSL_AND_CERTIFICATES_WRITE },
                            { "id": DNS_WRITE },
                        ],
                    }),
                ],
                Some(expires_on),
            )
            .await?;
        Ok(TemporaryToken { id, value })
    }

    async fn revoke_token(&self, purpose: &str, id: &str) -> Result<()> {
        revoke_token(&self.client, &self.setup_token, id)
            .await
            .with_context(|| format!("the {purpose} token"))
    }

    /// The convenient path: one `API Tokens -> Edit` token, everything else
    /// minted here and the provisioning token revoked on the way out.
    pub async fn run_managed(
        &self,
        project_id: &str,
        app_origin: &str,
        app_hostname: &str,
    ) -> Result<(
        ProvisionedResources,
        ConnectCredentials,
        MintedCredentialIds,
    )> {
        self.verify().await?;
        let provisioning = self.mint_provisioning_token(project_id).await?;
        let result = async {
            let resources = self
                .provision(&provisioning.value, project_id, app_origin, app_hostname)
                .await?;
            let (credentials, minted) = self.mint_credentials(project_id, &resources).await?;
            Ok((resources, credentials, minted))
        }
        .await;
        // Best effort, and reported rather than swallowed: the token expires on
        // its own, but a user who has to wait for that should know why.
        if let Err(error) = self.revoke_token("provisioning", &provisioning.id).await {
            eprintln!(
                "warning: {error}. It expires by itself within \
                 {PROVISIONING_TOKEN_MINUTES} minutes."
            );
        }
        result
    }

    /// The careful path: provision with the token as given, mint nothing. The
    /// caller's token is expected to be unable to create tokens, which is the
    /// whole reason to choose this.
    pub async fn run_manual(
        &self,
        project_id: &str,
        app_origin: &str,
        app_hostname: &str,
    ) -> Result<ProvisionedResources> {
        self.verify().await?;
        self.provision(&self.setup_token, project_id, app_origin, app_hostname)
            .await
    }

    async fn provision(
        &self,
        token: &str,
        project_id: &str,
        app_origin: &str,
        app_hostname: &str,
    ) -> Result<ProvisionedResources> {
        let zone_name = self.zone_name(token).await?;

        let private_object_storage_bucket = private_object_storage_bucket_name(project_id);
        let public_object_storage_bucket = public_object_storage_bucket_name(project_id);
        let frontend_asset_bucket = frontend_asset_bucket_name(project_id);
        let frontend_asset_hostname = format!("{frontend_asset_bucket}.{zone_name}");
        let public_object_storage_hostname = format!("{public_object_storage_bucket}.{zone_name}");

        for bucket in [
            &private_object_storage_bucket,
            &public_object_storage_bucket,
            &frontend_asset_bucket,
        ] {
            self.create_bucket(token, bucket).await?;
        }
        for bucket in [
            &private_object_storage_bucket,
            &public_object_storage_bucket,
            &frontend_asset_bucket,
        ] {
            self.put_cors(token, bucket, Some(app_origin)).await?;
        }
        self.attach_custom_domain(token, &frontend_asset_bucket, &frontend_asset_hostname)
            .await?;
        self.attach_custom_domain(
            token,
            &public_object_storage_bucket,
            &public_object_storage_hostname,
        )
        .await?;
        self.ensure_cache_rule(token, &zone_name, Some(app_hostname), None)
            .await?;
        self.ensure_tiered_cache(token).await?;

        Ok(ProvisionedResources {
            zone_name,
            frontend_asset_hostname,
            public_object_storage_hostname,
            private_object_storage_bucket,
            public_object_storage_bucket,
            frontend_asset_bucket,
        })
    }

    fn bucket_scope(&self, buckets: &[&String]) -> serde_json::Value {
        let resources: serde_json::Map<String, serde_json::Value> = buckets
            .iter()
            .map(|bucket| {
                (
                    format!(
                        "com.cloudflare.edge.r2.bucket.{}_default_{bucket}",
                        self.account_id
                    ),
                    serde_json::Value::String("*".to_string()),
                )
            })
            .collect();
        serde_json::json!({
            "effect": "allow",
            "resources": resources,
            "permission_groups": [
                { "id": R2_BUCKET_ITEM_READ },
                { "id": R2_BUCKET_ITEM_WRITE },
            ],
        })
    }

    async fn mint_credentials(
        &self,
        project_id: &str,
        resources: &ProvisionedResources,
    ) -> Result<(ConnectCredentials, MintedCredentialIds)> {
        let (worker_access_key_id, worker_token) = self
            .mint_with_expiry(
                &format!("fn0 worker ({project_id})"),
                vec![self.bucket_scope(&[
                    &resources.private_object_storage_bucket,
                    &resources.public_object_storage_bucket,
                ])],
                None,
            )
            .await?;

        let (frontend_asset_access_key_id, frontend_asset_token) = self
            .mint_with_expiry(
                &format!("fn0 frontend assets ({project_id})"),
                vec![self.bucket_scope(&[&resources.frontend_asset_bucket])],
                None,
            )
            .await?;

        let (purge_token_id, purge_token) = self
            .mint_with_expiry(
                &format!("fn0 cache purge ({project_id})"),
                vec![serde_json::json!({
                    "effect": "allow",
                    "resources": {
                        format!("com.cloudflare.api.account.zone.{}", self.zone_id): "*",
                    },
                    "permission_groups": [{ "id": CACHE_PURGE }],
                })],
                None,
            )
            .await?;

        let minted = MintedCredentialIds {
            worker: worker_access_key_id.clone(),
            frontend_asset: frontend_asset_access_key_id.clone(),
            purge: purge_token_id,
        };
        Ok((
            ConnectCredentials {
                worker_access_key_id,
                worker_secret: hex_sha256(&worker_token),
                frontend_asset_access_key_id,
                frontend_asset_secret: hex_sha256(&frontend_asset_token),
                purge_token,
            },
            minted,
        ))
    }

    /// Best effort, and reported rather than swallowed: unlike the provisioning
    /// token these carry no expiry, so one left behind stays until the user
    /// finds it.
    pub async fn revoke_minted_credentials(&self, ids: &MintedCredentialIds) {
        for (purpose, id) in [
            ("worker", &ids.worker),
            ("frontend assets", &ids.frontend_asset),
            ("cache purge", &ids.purge),
        ] {
            if let Err(error) = self.revoke_token(purpose, id).await {
                eprintln!("warning: {error}. Delete it in the Cloudflare dashboard.");
            }
        }
    }

    /// Signs an origin certificate for `hostname` through the zone owner's own
    /// Origin CA.
    ///
    /// The key pair is generated here and the private key is sent to fn0
    /// alongside the certificate, because the worker has to present it during
    /// the TLS handshake. Nothing that can sign another one is: the token that
    /// did the signing is revoked before this returns.
    pub async fn issue_origin_certificate(
        &self,
        hostname: &str,
        mint_signing_token: bool,
    ) -> Result<IssuedCertificate> {
        self.verify().await?;
        if !mint_signing_token {
            return self
                .sign_origin_certificate(&self.setup_token, hostname)
                .await;
        }
        let signing = self.mint_provisioning_token(hostname).await?;
        let result = self.sign_origin_certificate(&signing.value, hostname).await;
        if let Err(error) = self.revoke_token("signing", &signing.id).await {
            eprintln!(
                "warning: {error}. It expires by itself within \
                 {PROVISIONING_TOKEN_MINUTES} minutes."
            );
        }
        result
    }

    /// Repoints the buckets' CORS at a domain the project has moved to.
    /// Provisioning writes the same rules for the domain the project starts
    /// with; this is how they follow it afterwards.
    pub async fn put_app_cors(
        &self,
        project_id: &str,
        app_origin: &str,
        mint_writing_token: bool,
    ) -> Result<()> {
        let buckets = [
            private_object_storage_bucket_name(project_id),
            public_object_storage_bucket_name(project_id),
            frontend_asset_bucket_name(project_id),
        ];
        if !mint_writing_token {
            for bucket in &buckets {
                self.put_cors(&self.setup_token, bucket, Some(app_origin))
                    .await?;
            }
            return Ok(());
        }
        let writing = self.mint_provisioning_token(app_origin).await?;
        let result = async {
            for bucket in &buckets {
                self.put_cors(&writing.value, bucket, Some(app_origin))
                    .await?;
            }
            Ok(())
        }
        .await;
        if let Err(error) = self.revoke_token("CORS", &writing.id).await {
            eprintln!(
                "warning: {error}. It expires by itself within \
                 {PROVISIONING_TOKEN_MINUTES} minutes."
            );
        }
        result
    }

    async fn sign_origin_certificate(
        &self,
        token: &str,
        hostname: &str,
    ) -> Result<IssuedCertificate> {
        #[derive(Serialize)]
        struct Body<'a> {
            csr: &'a str,
            hostnames: [&'a str; 1],
            request_type: &'a str,
            requested_validity: u32,
        }
        #[derive(Deserialize)]
        struct Certificate {
            certificate: String,
        }

        let key_pair = rcgen::KeyPair::generate()
            .map_err(|error| anyhow!("could not generate a key pair: {error}"))?;
        let mut params = rcgen::CertificateParams::new(vec![hostname.to_string()])
            .map_err(|error| anyhow!("could not build the certificate request: {error}"))?;
        params.distinguished_name = rcgen::DistinguishedName::new();
        params
            .distinguished_name
            .push(rcgen::DnType::CommonName, hostname);
        let csr_pem = params
            .serialize_request(&key_pair)
            .map_err(|error| anyhow!("could not sign the certificate request: {error}"))?
            .pem()
            .map_err(|error| anyhow!("could not encode the certificate request: {error}"))?;

        let (status, envelope) = self
            .call::<Certificate>(
                token,
                reqwest::Method::POST,
                "/certificates",
                Some(serde_json::to_value(Body {
                    csr: &csr_pem,
                    hostnames: [hostname],
                    request_type: CERTIFICATE_REQUEST_TYPE,
                    requested_validity: CERTIFICATE_VALIDITY_DAYS,
                })?),
            )
            .await?;
        let certificate = envelope
            .result
            .filter(|_| envelope.success)
            .ok_or_else(|| {
                anyhow!(
                    "Cloudflare would not sign the origin certificate ({status}): {}",
                    describe(&envelope.errors)
                )
            })?;

        Ok(IssuedCertificate {
            certificate_pem: certificate.certificate,
            private_key_pem: key_pair.serialize_pem(),
            // Derived rather than parsed out of the response: Cloudflare answers
            // with a Go-formatted timestamp, and the validity we asked for is
            // the same fact without a format to get wrong.
            not_after_epoch_seconds: chrono::Utc::now().timestamp()
                + i64::from(CERTIFICATE_VALIDITY_DAYS) * SECONDS_PER_DAY,
        })
    }
}

/// R2's S3 API takes the SHA-256 of the token value as the secret access key,
/// lowercase hex — the same string `printf '%s' <token> | sha256sum` produces.
fn cache_rule_app_hostnames(rule: &serde_json::Value) -> BTreeSet<String> {
    let Some(expression) = rule.get("expression").and_then(|value| value.as_str()) else {
        return BTreeSet::new();
    };
    if let Some(hostname) = expression
        .split_once("http.host eq \"")
        .and_then(|(_, remainder)| remainder.split_once('"'))
        .map(|(hostname, _)| hostname)
    {
        return BTreeSet::from([hostname.to_string()]);
    }
    let Some(host_list) = expression
        .split_once("http.host in {")
        .and_then(|(_, remainder)| remainder.split_once('}'))
        .map(|(host_list, _)| host_list)
    else {
        return BTreeSet::new();
    };
    host_list
        .split('"')
        .skip(1)
        .step_by(2)
        .filter(|hostname| !hostname.is_empty())
        .map(str::to_string)
        .collect()
}

fn cache_rule_host_expression(zone_name: &str, app_hostnames: &BTreeSet<String>) -> String {
    let mut host_expressions = vec![
        format!(r#"http.host wildcard "fn0-*-frontend-asset.{zone_name}""#),
        format!(r#"http.host wildcard "fn0-*-public-object-storage.{zone_name}""#),
    ];
    if !app_hostnames.is_empty() {
        let exact_hostnames = app_hostnames
            .iter()
            .map(|hostname| format!(r#""{hostname}""#))
            .collect::<Vec<_>>()
            .join(" ");
        host_expressions.push(format!("http.host in {{{exact_hostnames}}}"));
    }
    host_expressions.join(" or ")
}

#[derive(Deserialize)]
struct DnsRecord {
    id: String,
    #[serde(rename = "type")]
    record_type: String,
    content: String,
    /// Absent on the record types that cannot be proxied at all.
    #[serde(default)]
    proxied: bool,
}

enum AppDnsRecordWrite<'a> {
    AlreadyPointed,
    Create,
    Repoint {
        record_id: &'a str,
    },
    /// Held by records a CNAME cannot join: Cloudflare refuses an A next to a
    /// CNAME on one name, and refuses a second record of either kind.
    Occupied {
        record_types: String,
    },
}

/// A CNAME already on the hostname is repointed rather than refused. The user
/// named this hostname on the command line, so where it resolves is what they
/// are asking to change; an address record of another type is a different
/// enough thing to stop for.
fn decide_app_dns_record<'a>(
    records: &'a [DnsRecord],
    origin_hostname: &str,
) -> AppDnsRecordWrite<'a> {
    let resolving: Vec<&DnsRecord> = records
        .iter()
        .filter(|record| matches!(record.record_type.as_str(), "A" | "AAAA" | "CNAME"))
        .collect();
    match resolving.as_slice() {
        [] => AppDnsRecordWrite::Create,
        [record] if record.record_type == "CNAME" => {
            if record.content == origin_hostname && record.proxied {
                AppDnsRecordWrite::AlreadyPointed
            } else {
                AppDnsRecordWrite::Repoint {
                    record_id: &record.id,
                }
            }
        }
        _ => AppDnsRecordWrite::Occupied {
            record_types: resolving
                .iter()
                .map(|record| record.record_type.as_str())
                .collect::<Vec<_>>()
                .join(", "),
        },
    }
}

fn replaced_app_dns_record<'a>(
    records: &'a [DnsRecord],
    origin_hostname: &str,
) -> Option<&'a DnsRecord> {
    records.iter().find(|record| {
        record.record_type == "CNAME" && record.proxied && record.content == origin_hostname
    })
}

fn hex_sha256(value: &str) -> String {
    let digest = Sha256::digest(value.as_bytes());
    let mut out = String::with_capacity(digest.len() * 2);
    for byte in digest {
        out.push_str(&format!("{byte:02x}"));
    }
    out
}

/// Deliberately does not accept "already in use": Cloudflare answers that when a
/// hostname is attached to a *different* bucket, which is a failure to report
/// rather than a step to skip. Treating it as success ends in a hostname that
/// resolves and serves 404 for every object.
/// `10059 The CORS configuration does not exist.`, measured.
fn cors_absent(errors: &[ApiError]) -> bool {
    errors.iter().any(|error| error.code == 10059)
}

fn already_exists(errors: &[ApiError]) -> bool {
    errors.iter().any(|error| {
        let message = error.message.to_lowercase();
        message.contains("already exists")
            || message.contains("already configured")
            || message.contains("duplicate")
    })
}

#[cfg(test)]
mod tests {
    use super::{
        AppDnsRecordWrite, DnsRecord, cache_rule_app_hostnames, cache_rule_host_expression,
        decide_app_dns_record, replaced_app_dns_record,
    };
    use std::collections::BTreeSet;

    const ORIGIN: &str = "worker.fn0.dev";

    fn record(record_type: &str, content: &str, proxied: bool) -> DnsRecord {
        DnsRecord {
            id: format!("id-{record_type}-{content}"),
            record_type: record_type.to_string(),
            content: content.to_string(),
            proxied,
        }
    }

    #[test]
    fn app_dns_record_is_created_when_the_hostname_is_free() {
        assert!(matches!(
            decide_app_dns_record(&[], ORIGIN),
            AppDnsRecordWrite::Create
        ));
    }

    #[test]
    fn app_dns_record_already_pointed_is_left_alone() {
        let records = [
            record("CNAME", ORIGIN, true),
            record("TXT", "some verification string", false),
        ];

        assert!(matches!(
            decide_app_dns_record(&records, ORIGIN),
            AppDnsRecordWrite::AlreadyPointed
        ));
    }

    #[test]
    fn app_dns_record_is_repointed_when_it_is_grey_or_aimed_elsewhere() {
        for records in [
            [record("CNAME", ORIGIN, false)],
            [record("CNAME", "somewhere.example.com", true)],
        ] {
            let AppDnsRecordWrite::Repoint { record_id } = decide_app_dns_record(&records, ORIGIN)
            else {
                panic!("expected a repoint");
            };
            assert_eq!(record_id, records[0].id);
        }
    }

    #[test]
    fn app_dns_record_refuses_an_address_record_it_cannot_repoint() {
        let records = [record("A", "203.0.113.7", true)];

        let AppDnsRecordWrite::Occupied { record_types } = decide_app_dns_record(&records, ORIGIN)
        else {
            panic!("expected the hostname to read as occupied");
        };
        assert_eq!(record_types, "A");
    }

    #[test]
    fn replaced_app_dns_record_matches_only_the_record_fn0_wrote() {
        assert!(
            replaced_app_dns_record(&[record("CNAME", ORIGIN, true)], ORIGIN)
                .is_some_and(|found| found.content == ORIGIN)
        );
        for records in [
            [record("CNAME", ORIGIN, false)],
            [record("CNAME", "somewhere.example.com", true)],
            [record("A", "203.0.113.7", true)],
        ] {
            assert!(replaced_app_dns_record(&records, ORIGIN).is_none());
        }
    }

    #[test]
    fn cache_rule_expression_contains_bucket_and_app_hosts() {
        let app_hostnames =
            BTreeSet::from(["app.example.com".to_string(), "www.example.com".to_string()]);

        assert_eq!(
            cache_rule_host_expression("example.com", &app_hostnames),
            r#"http.host wildcard "fn0-*-frontend-asset.example.com" or http.host wildcard "fn0-*-public-object-storage.example.com" or http.host in {"app.example.com" "www.example.com"}"#
        );
    }

    #[test]
    fn cache_rule_app_hostnames_reads_managed_rule_expression() {
        let rule = serde_json::json!({
            "expression": r#"((http.host wildcard "fn0-*-frontend-asset.example.com" or http.host in {"app.example.com" "www.example.com"}) and http.request.method in {"GET" "HEAD" "PURGE"})"#
        });

        assert_eq!(
            cache_rule_app_hostnames(&rule),
            BTreeSet::from(["app.example.com".to_string(), "www.example.com".to_string(),])
        );
    }

    #[test]
    fn cache_rule_app_hostnames_reads_single_host_expression() {
        let rule = serde_json::json!({
            "expression": r#"http.host eq "control.example.com""#
        });

        assert_eq!(
            cache_rule_app_hostnames(&rule),
            BTreeSet::from(["control.example.com".to_string()])
        );
    }
}