qh3_mutual_tls_patch

Runtime monkey-patch that adds mutual TLS (client certificate authentication) support to qh3's server-side TLS 1.3 implementation.

Problem

qh3's TLS 1.3 server does not send a CertificateRequest message during the handshake, so the client never presents its certificate. This makes it impossible to use mutual TLS authentication in QUIC servers built with qh3.

Solution

This package patches qh3's Context class at runtime to:

1. Inject a CertificateRequest message into the server handshake (after EncryptedExtensions, before Certificate)
2. Handle the client's Certificate, CertificateVerify, and Finished messages
3. Verify the client's certificate signature using Ed25519

The patch is non-destructive: connections with verify_mode = ssl.CERT_NONE are unaffected.

Installation

pip install qh3_mutual_tls_patch

Or install from source:

pip install .

Usage

Call apply() once before creating any QUIC connections:

import ssl
from qh3_mutual_tls_patch import apply
from qh3.quic.configuration import QuicConfiguration

# Apply the patch (safe to call multiple times)
apply()

# Now you can request client certificates on the server side
config = QuicConfiguration(is_client=False)
config.verify_mode = ssl.CERT_OPTIONAL  # or ssl.CERT_REQUIRED
# ... set certificate, private_key, alpn_protocols, etc.

After the handshake, the client's certificate is available via context.get_peercert().

How it works

The patch hooks three internal qh3 functions:

• push_encrypted_extensions — sets a flag after EncryptedExtensions is written
• push_message — intercepts the next push_message call (for the server Certificate) to inject CertificateRequest with its own transcript hash scope beforehand
• _server_handle_hello — wraps the original to restore the key-schedule hash after qh3's Finished-anticipation step, then transitions to custom states

Two custom TLS states (SERVER_EXPECT_CLIENT_CERT and SERVER_EXPECT_CLIENT_CERT_VERIFY) handle the client's response before handing control back to qh3's SERVER_EXPECT_FINISHED state.

Compatibility

• qh3 >= 1.2.1
• Python >= 3.10

Limitations

• Only Ed25519 is advertised in the CertificateRequest signature algorithms extension.
• The patch relies on qh3 internals and may break with future qh3 releases.

License

MIT