Add support for MSN with X-MESSENGER-OAUTH2 SASL support.

NOTE: This requires already having the access token. It does NOT
perform any OAuth requests.

sleekxmpp/thirdparty/suelta/mechanisms/messenger_oauth2.py

@@ -0,0 +1,18 @@
+from sleekxmpp.thirdparty.suelta.util import hash, bytes
+from sleekxmpp.thirdparty.suelta.sasl import Mechanism, register_mechanism
+from sleekxmpp.thirdparty.suelta.exceptions import SASLError, SASLCancelled
+
+
+class X_MESSENGER_OAUTH2(Mechanism):
+
+    def __init__(self, sasl, name):
+        super(X_MESSENGER_OAUTH2, self).__init__(sasl, name)
+        self.check_values(['access_token'])
+
+    def process(self, challenge=None):
+        return self.values['access_token']
+
+    def okay(self):
+        return True
+
+register_mechanism('X-MESSENGER-OAUTH2', 10, X_MESSENGER_OAUTH2, use_hashes=False)