Adding EXTERNAL mechanism

README.rst

@@ -6,7 +6,7 @@ pure-sasl
 
 pure-sasl is a pure python client-side SASL implementation.
 
-At the moment, it supports the following mechanisms: ANONYMOUS, PLAIN,
+At the moment, it supports the following mechanisms: ANONYMOUS, PLAIN, EXTERNAL,
 CRAM-MD5, DIGEST-MD5, and GSSAPI. Support for other mechanisms may be added in the
 future. Only GSSAPI supports a QOP higher than auth. Always use TLS!
 

puresasl/mechanisms.py

@@ -172,6 +172,25 @@ def dispose(self):
         self.password = None
 
 
+class ExternalMechanism(Mechanism):
+    """
+    The EXTERNAL mechanism allows a client to request the server to use
+    credentials established by means external to the mechanism to
+    authenticate the client.
+    """
+    name = 'EXTERNAL'
+    score = 10
+
+    def wrap(self, outgoing):
+        return outgoing
+
+    def unwrap(self, incoming):
+        return incoming
+
+    def process(self, challenge=None):
+        return b''
+
+
 class CramMD5Mechanism(PlainMechanism):
     name = "CRAM-MD5"
     score = 20
@@ -530,6 +549,7 @@ def dispose(self):
 mechanisms = dict((m.name, m) for m in (
     AnonymousMechanism,
     PlainMechanism,
+    ExternalMechanism,
     CramMD5Mechanism,
     DigestMD5Mechanism))
 

setup.py

@@ -15,7 +15,7 @@
       long_description=
 """This package provides a reasonably high-level SASL client written
 in pure Python.  New mechanisms may be integrated easily, but by default,
-support for PLAIN, ANONYMOUS, CRAM-MD5, DIGEST-MD5, and GSSAPI are
+support for PLAIN, ANONYMOUS, EXTERNAL, CRAM-MD5, DIGEST-MD5, and GSSAPI are
 provided.""",
       license='MIT',
       url='http://github.com/thobbs/pure-sasl',

tests/unit/test_mechanism.py

@@ -14,7 +14,7 @@
 
 from puresasl import SASLProtocolException, QOP
 from puresasl.client import SASLClient
-from puresasl.mechanisms import AnonymousMechanism, PlainMechanism, GSSAPIMechanism, DigestMD5Mechanism, CramMD5Mechanism
+from puresasl.mechanisms import AnonymousMechanism, PlainMechanism, GSSAPIMechanism, DigestMD5Mechanism, CramMD5Mechanism, ExternalMechanism
 
 
 class _BaseMechanismTests(unittest.TestCase):
@@ -91,6 +91,20 @@ def test_wrap_unwrap(self):
         self.assertIs(self.sasl.wrap(msg), msg)
         self.assertIs(self.sasl.unwrap(msg), msg)
 
+
+class ExternalMechanismTest(_BaseMechanismTests):
+
+    mechanism_class = ExternalMechanism
+
+    def test_process(self):
+        self.assertIs(self.sasl.process(), b'')
+
+    def test_wrap_unwrap(self):
+        msg = 'msg'
+        self.assertIs(self.sasl.wrap(msg), msg)
+        self.assertIs(self.sasl.unwrap(msg), msg)
+
+
 @patch('puresasl.mechanisms.kerberos.authGSSClientStep')
 @patch('puresasl.mechanisms.kerberos.authGSSClientResponse', return_value=base64.b64encode(six.b('some\x00 response')))
 class GSSAPIMechanismTest(_BaseMechanismTests):