Add XSRF protection to oauth2decorator callback.
Also update all samples to use XSRF callback protection.

Reviewed in https://codereview.appspot.com/6473053/.
diff --git a/tests/test_oauth2client_xsrfutil.py b/tests/test_oauth2client_xsrfutil.py
new file mode 100644
index 0000000..a86a15b
--- /dev/null
+++ b/tests/test_oauth2client_xsrfutil.py
@@ -0,0 +1,111 @@
+# Copyright 2012 Google Inc.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+"""Tests for oauth2client.xsrfutil.
+
+Unit tests for oauth2client.xsrfutil.
+"""
+
+__author__ = 'jcgregorio@google.com (Joe Gregorio)'
+
+import unittest
+
+from oauth2client import xsrfutil
+
+# Jan 17 2008, 5:40PM
+TEST_KEY = 'test key'
+TEST_TIME = 1200609642081230
+TEST_USER_ID_1 = 123832983
+TEST_USER_ID_2 = 938297432
+TEST_ACTION_ID_1 = 'some_action'
+TEST_ACTION_ID_2 = 'some_other_action'
+TEST_EXTRA_INFO_1 = 'extra_info_1'
+TEST_EXTRA_INFO_2 = 'more_extra_info'
+
+
+class XsrfUtilTests(unittest.TestCase):
+  """Test xsrfutil functions."""
+
+  def testGenerateAndValidateToken(self):
+    """Test generating and validating a token."""
+    token = xsrfutil.generate_token(TEST_KEY,
+                                   TEST_USER_ID_1,
+                                   action_id=TEST_ACTION_ID_1,
+                                   when=TEST_TIME)
+
+    # Check that the token is considered valid when it should be.
+    self.assertTrue(xsrfutil.validate_token(TEST_KEY,
+                                           token,
+                                           TEST_USER_ID_1,
+                                           action_id=TEST_ACTION_ID_1,
+                                           current_time=TEST_TIME))
+
+    # Should still be valid 15 minutes later.
+    later15mins = TEST_TIME + 15*60
+    self.assertTrue(xsrfutil.validate_token(TEST_KEY,
+                                           token,
+                                           TEST_USER_ID_1,
+                                           action_id=TEST_ACTION_ID_1,
+                                           current_time=later15mins))
+
+    # But not if beyond the timeout.
+    later2hours = TEST_TIME + 2*60*60
+    self.assertFalse(xsrfutil.validate_token(TEST_KEY,
+                                            token,
+                                            TEST_USER_ID_1,
+                                            action_id=TEST_ACTION_ID_1,
+                                            current_time=later2hours))
+
+    # Or if the key is different.
+    self.assertFalse(xsrfutil.validate_token('another key',
+                                            token,
+                                            TEST_USER_ID_1,
+                                            action_id=TEST_ACTION_ID_1,
+                                            current_time=later15mins))
+
+    # Or the user ID....
+    self.assertFalse(xsrfutil.validate_token(TEST_KEY,
+                                            token,
+                                            TEST_USER_ID_2,
+                                            action_id=TEST_ACTION_ID_1,
+                                            current_time=later15mins))
+
+    # Or the action ID...
+    self.assertFalse(xsrfutil.validate_token(TEST_KEY,
+                                            token,
+                                            TEST_USER_ID_1,
+                                            action_id=TEST_ACTION_ID_2,
+                                            current_time=later15mins))
+
+    # Invalid when truncated
+    self.assertFalse(xsrfutil.validate_token(TEST_KEY,
+                                            token[:-1],
+                                            TEST_USER_ID_1,
+                                            action_id=TEST_ACTION_ID_1,
+                                            current_time=later15mins))
+
+    # Invalid with extra garbage
+    self.assertFalse(xsrfutil.validate_token(TEST_KEY,
+                                            token + 'x',
+                                            TEST_USER_ID_1,
+                                            action_id=TEST_ACTION_ID_1,
+                                            current_time=later15mins))
+
+    # Invalid with token of None
+    self.assertFalse(xsrfutil.validate_token(TEST_KEY,
+                                             None,
+                                             TEST_USER_ID_1,
+                                             action_id=TEST_ACTION_ID_1))
+
+if __name__ == '__main__':
+  unittest.main()