The IRC relay protocol's PASS handler compared the server password with
the client-supplied value using strcmp, leaking the password byte-by-byte
via response timing. This is the same class of bug fixed for the api and
weechat protocols, on a separate code path that did not go through
relay_auth_check_password_plain.
Extract the HMAC-then-constant-time-compare logic from
relay_auth_check_password_plain into relay_auth_password_equals, then
use it in both the plain-auth wrapper and the IRC PASS handler.
This introduces a new command called "handshake" in the weechat relay protocol.
It should be sent by the client before the "init" command, to negotiate the way
to authenticate with a password.
3 new options are added:
* relay.network.auth_password
* relay.network.hash_iterations
* relay.network.nonce_size
Sébastien Helleu