TLS server: client-certificate request path is inert

[ChristopherA]

The server session accepts a reqCert flag (src/usr/TLS/api/lib/ServerSession.c, void accept(int reqCert, string hosts...)), but sendCertificateRequest() has an empty body (line ~143), so no CertificateRequest message is ever produced and the certificate-verification wait states are unreachable. As a result, mutual TLS cannot be enabled through the documented parameter -- it behaves as a no-op.

Is client-certificate authentication intended to be unimplemented for now? If so, a comment on accept() noting the parameter is reserved would prevent misreading; if not, happy to provide more detail on what we observed while testing.

[dworkin]

Client certificate is indeed unimplemented. TheTLS implementation originates as a minimal implementation to get signal-server working, and client certificates are not needed there.

I do intend to implement it in the future.