sessionRemoteIdentityKey
open override fun sessionRemoteIdentityKey(session: SecureSession, localIdentityKey: ByteArray): ByteArray?
The remote identity key session was established with, or null if that cannot be told apart from the local one: exactly one of the session's two identity keys must equal localIdentityKey, and the other one is returned. Never returns the local key. Used to pin a session created before identity pinning (S1, finding F9).