proposal: crypto/tls: add SetOCSPStaple function

[gregory-m]

OCSPStaple should be updated by server after it expiration.
Today we can't update it directly without data races, and the only one workaround is use tls.Config.GetCertificate and return certificate with OCSPStaple populated.

Can we add SetOCSPStaple function with mutex to tls.Certificate (just like SetSessionTicketKeys) to simplify this?

Thanks.

[bradfitz]

/cc @agl

[adg]

Ping @agl. Does this make sense?

[adg]

Ping

[agl]

Yes, this makes sense. I had originally expected people to atomically switch the tls.Config for this sort of thing, but that doesn't appear to be how things are working out.

[kreichgauer]

Chatted with @agl about this. tls.Certificate is occasionally passed by value (e.g., tls.LoadX509KeyPair returns a Certificate; tls.Config.Certificates is a []tls.Certificate). So we would end up copying mutexes in a few places. AFAICT this is technically okay because copies would be made shortly after initialization (i.e. before anyone could reasonably call SetOCSPStaple). Though I don't know if this would pass review.

Alternatively, we could add a GetOCSPStable callback, returning a staple for a given certificate. But would either solution really add much convenience over using GetCertificate? Maybe improving documentation of Certificate.OCSPStaple is a better solution.