Adding a check of string type for hmacs

- To ensure comparison is done on binary data

The method would first check if the 2 hmacs are a python
`six.stringtype`. If they are, they would be encoded using
'utf-8' as the encoding scheme to binary data.

Change-Id: Idf59f669087a39c30eee4e533899b95ede66e198

oslo_utils/secretutils.py

@@ -14,6 +14,8 @@
 
 import hmac
 
+import six
+
 
 try:
     constant_time_compare = hmac.compare_digest
@@ -27,6 +29,10 @@ except AttributeError:
         content-based short circuiting behaviour, making it appropriate
         for cryptography.
         """
+        if isinstance(first, six.string_types):
+            first = first.encode('utf-8')
+        if isinstance(second, six.string_types):
+            second = second.encode('utf-8')
         if len(first) != len(second):
             return False
         result = 0

oslo_utils/tests/test_secretutils.py

@@ -34,6 +34,7 @@ class SecretUtilsTest(testscenarios.TestWithScenarios,
                             self.converter(u'abcd')))
         self.assertTrue(ctc(self.converter(u''),
                             self.converter(u'')))
+        self.assertTrue(ctc('abcd', 'abcd'))
         self.assertFalse(ctc(self.converter(u'abcd'),
                              self.converter(u'efgh')))
         self.assertFalse(ctc(self.converter(u'abc'),
@@ -50,3 +51,4 @@ class SecretUtilsTest(testscenarios.TestWithScenarios,
                              self.converter(u'a')))
         self.assertFalse(ctc(self.converter(u'abcd1234'),
                              self.converter(u'1234abcd')))
+        self.assertFalse(ctc('abcd1234', '1234abcd'))