How to use the sasl.Plain function in sasl

os.setuid(userinfo[2])
    except:
        Log.error("Failed to find user 'bbs'!")
        sys.exit(1)

    Config.Config.LoadConfig();
    UCache.UCache.Init()
    Utmp.Utmp.Init()
    commondata.CommonData.Init()

    hostname = Config.Config.GetString("BBS_XMPP_HOST", 'localhost')

    server = xmpp.Server({
        'plugins': [(xmppserver.XMPPServer, { 'rosters': rosters.Rosters() , 'host': hostname})],
        'auth': xmppauth.XMPPAuth('xmpp', hostname, 'bbs'),
        'mechanisms': (sasl.Plain, bbsauth.BBSAuth),
        'certfile': Config.BBS_XMPP_CERT_FILE,
        'keyfile': Config.BBS_XMPP_KEY_FILE,
    })

    SP = xmpp.TCPServer(server).bind('0.0.0.0', 5222)
    xmpp.start([SP])

## ---------- Common ----------

    def negotiate(self):
        self.starttls(self.done, **self.options)

    def done(self):
        self._active = False
        self.trigger(StreamSecured).reset_stream()


### SASL

class Mechanisms(plugin.Feature):
    __xmlns__ = 'urn:ietf:params:xml:ns:xmpp-sasl'

    DEFAULT_MECHANISMS = (sasl.Plain, )

    def __init__(self, auth, mechanisms=None):
        self.auth = auth
        self.mechanisms = mechanisms or self.DEFAULT_MECHANISMS
        self.jid = None

    def active(self):
        return not self.jid

    ## ---------- Server ----------

    def include(self):
        self.bind(
            auth=self.begin,
            abort=self.terminate,
            success=self.terminate,