Support with SASL login methods

[Rhialto]

Hi! I notice there is a sasl_login() method, to which you give one mechanism. The tricky part is to know which mechanism is supported by the server, since (as far as I know) it doesn't tell you. You have to guess, and try a few.
Since the method throws an exception when the mechanism isn't supported, this gets a bit annoying, flow-control wise.
Also, there are no given authentication mechanisms to try. Creating one for CRAM-MD5 wasn't so difficult (see below), but I expect that I will need a few more, if I want to connect to other servers than just my own.
Is there some help available to try to iterate over several login methods and their associated mechanism code?

Here is a CRAM-MD5 implementation that worked for me.

class CramMD5SaslMechanism():
    def __init__(self, username, password):
        self.username = username
        self.password = password
        self.step = 0

    def __call__(self, challenge):
        self.step += 1
        if self.step == 1:
            logging.debug("challenge = %s", challenge)
            response = self.cram_md5(self.username, self.password, challenge)
        return response

    def cram_md5(self, user, password, challenge):
        password = password.encode('utf-8')
        digest = hmac.HMAC(password, challenge, hashlib.md5).hexdigest()
        response = '{} {}'.format(user, digest)
        logging.debug("response = %s", response)
        return response