Add support for verifying certificate chain with EKU

src/end_entity.rs

@@ -181,4 +181,39 @@ impl<'a> EndEntityCert<'a> {
             untrusted::Input::from(signature),
         )
     }
+
+    /// Verifies that the end-entity certificate is valid for use by cert chain
+    ///
+    /// `required_eku` is the Certificate Extended Key Usage Oid in bytes.
+    /// If the certificate is not valid for `required_eku` then this
+    /// fails with `Error::CertNotValidForName`.
+    /// `supported_sig_algs` is the list of signature algorithms that are
+    /// trusted for use in certificate signatures; the end-entity certificate's
+    /// public key is not validated against this list. `trust_anchors` is the
+    /// list of root CAs to trust. `intermediate_certs` is the sequence of
+    /// intermediate certificates that the client sent in the TLS handshake.
+    /// `cert` is the purported end-entity certificate of the client. `time` is
+    /// the time for which the validation is effective (usually the current
+    /// time).
+    ///
+    pub fn verify_is_valid_cert_with_eku(
+        &self,
+        required_eku: &'static [u8],
+        supported_sig_algs: &[&SignatureAlgorithm],
+        trust_anchors: &[crate::TrustAnchor],
+        intermediate_certs: &[&[u8]],
+        time: Time,
+    ) -> Result<(), Error> {
+        let eku = verify_cert::KeyPurposeId::new(required_eku);
+
+        crate::verify_cert::build_chain(
+            eku,
+            supported_sig_algs,
+            trust_anchors,
+            intermediate_certs,
+            &self.inner,
+            time,
+            0,
+        )
+    }
 }

src/verify_cert.rs

@@ -257,6 +257,22 @@ pub struct KeyPurposeId {
     oid_value: untrusted::Input<'static>,
 }
 
+impl KeyPurposeId {
+    /// Construct a new `KeyPurposeId`
+    ///
+    /// `oid` is the OBJECT IDENTIFIER in bytes.
+    ///
+    /// For example:
+    /// static EKU_SERVER_AUTH_BYTES: &'static [u8] = &[(40 * 1) + 3, 6, 1, 5, 5, 7, 3, 1];
+    /// let oid = KeyPurposeId::new(EKU_SERVER_AUTH_BYTES);
+    ///
+    pub fn new(oid: &'static [u8]) -> Self {
+        KeyPurposeId {
+            oid_value: untrusted::Input::from(oid),
+        }
+    }
+}
+
 // id-pkix            OBJECT IDENTIFIER ::= { 1 3 6 1 5 5 7 }
 // id-kp              OBJECT IDENTIFIER ::= { id-pkix 3 }