Add support for X-FACEBOOK-PLATFORM SASL mechanism.

This requires an extra credential for SASL authentication:

xmpp = ClientXMPP('user@chat.facebook.com', '...access_token...')
xmpp.credentials['api_key'] = '...api_key...'

sleekxmpp/thirdparty/suelta/mechanisms/__init__.py

@@ -4,3 +4,4 @@ from sleekxmpp.thirdparty.suelta.mechanisms.cram_md5 import CRAM_MD5
 from sleekxmpp.thirdparty.suelta.mechanisms.digest_md5 import DIGEST_MD5
 from sleekxmpp.thirdparty.suelta.mechanisms.scram_hmac import SCRAM_HMAC
 from sleekxmpp.thirdparty.suelta.mechanisms.messenger_oauth2 import X_MESSENGER_OAUTH2
+from sleekxmpp.thirdparty.suelta.mechanisms.facebook_platform import X_FACEBOOK_PLATFORM

sleekxmpp/thirdparty/suelta/mechanisms/facebook_platform.py

@@ -0,0 +1,39 @@
+from sleekxmpp.thirdparty.suelta.util import bytes
+from sleekxmpp.thirdparty.suelta.sasl import Mechanism, register_mechanism
+
+try:
+    import urlparse
+except ImportError:
+    import urllib.parse as urlparse
+
+
+
+class X_FACEBOOK_PLATFORM(Mechanism):
+
+    def __init__(self, sasl, name):
+        super(X_FACEBOOK_PLATFORM, self).__init__(sasl, name)
+        self.check_values(['access_token', 'api_key'])
+
+    def process(self, challenge=None):
+        if challenge is not None:
+            values = {}
+            for kv in challenge.split('&'):
+                key, value = kv.split('=')
+                values[key] = value
+
+            resp_data = {
+                'method': values['method'],
+                'v': '1.0',
+                'call_id': '1.0',
+                'nonce': values['nonce'],
+                'access_token': self.values['access_token'],
+                'api_key': self.values['api_key']
+            }
+            resp = '&'.join(['%s=%s' % (k, v) for k, v in resp_data.items()])
+            return bytes(resp)
+        return bytes('')
+
+    def okay(self):
+        return True
+
+register_mechanism('X-FACEBOOK-PLATFORM', 40, X_FACEBOOK_PLATFORM, use_hashes=False)