Give each CA its own CRL path

A verifier that cached the CRL of an earlier CA would otherwise apply it to a re-minted one.

core/src/mitm/ca.rs

@@ -1,4 +1,5 @@
 use rama::error::BoxError;
+use rama::tls::boring::core::sha::sha256;
 use rama::tls::boring::core::x509::X509;
 use rcgen::{
     BasicConstraints, CertificateParams, CertificateRevocationListParams, DistinguishedName,
@@ -39,6 +40,12 @@ impl CertificateAuthority {
         (held == signer.subject_public_key_info()).then_some(ca)
     }
 
+    /// Unique to this CA, so a verifier's cached CRL from an earlier one never applies to it.
+    pub fn crl_path(&self) -> String {
+        let digest = sha256(self.pem.as_bytes());
+        format!("/{}.crl", digest[..8].iter().map(|b| format!("{b:02x}")).collect::<String>())
+    }
+
     fn new(pem: String) -> Result<Self, BoxError> {
         Ok(Self { crt: X509::from_pem(pem.as_bytes())?, pem })
     }

core/tests/mitm.rs

@@ -50,3 +50,12 @@ fn ca_signs_an_empty_crl() {
     let crl = mitm::crl(&["registry.npmjs.org", "pypi.org"], &signer()).expect("sign a crl");
     assert_eq!(crl[0], 0x30, "a DER SEQUENCE");
 }
+
+/// A re-minted CA must not inherit the old one's CRL from a verifier's cache.
+#[test]
+fn each_ca_names_its_own_crl() {
+    let signer = signer();
+    let npm = mitm::CertificateAuthority::generate(&["registry.npmjs.org"], &signer).expect("mint a ca");
+    let pypi = mitm::CertificateAuthority::generate(&["pypi.org"], &signer).expect("mint a ca");
+    assert_ne!(npm.crl_path(), pypi.crl_path());
+}