Client.authenticate() should Base64 encode the data from the Authenticator

[kmkaplan]

RFC 3501 6.2.2. AUTHENTICATE Command says that

The client response consists of a single line consisting of a BASE64 encoded string.

So the Base64 encoding is really part of the IMAP protocol. The PLAIN SASL mecanism specification even does not show the encoding. That means that every Authenticator::process method has to do the Base64 encoding. It would be easier for everybody if that process was done inside Client.do_auth_handshake() for every Authenticator.

If that sounds reasonnable I can provide a pull request.

[jonhoo]

I agree, that seems reasonable! I'd be happy to review a PR.

[kmkaplan]

OK, I'll do that.