Fix py3 compatibility issue in PKCS#11 plugin

This patch fixes a str to char * type cast that is only valid
in Python 2.

Change-Id: Ia3bcfe125c4e2c49e8a3e2a4cdb2d67e641ceadd

barbican/plugin/crypto/pkcs11.py

@@ -16,6 +16,7 @@ import textwrap
 
 import cffi
 from cryptography.hazmat.primitives import padding
+import six
 
 from barbican.common import exception
 from barbican.common import utils
@@ -386,7 +387,7 @@ class PKCS11(object):
         self._check_error(rv)
 
         # Session options
-        self.login_passphrase = login_passphrase
+        self.login_passphrase = _to_bytes(login_passphrase)
         self.rw_session = rw_session
         self.slot_id = slot_id
 
@@ -795,3 +796,10 @@ class PKCS11(object):
         if test_random == b'\x00' * 100:
             raise exception.P11CryptoPluginException(
                 u._("Apparent RNG self-test failure."))
+
+
+def _to_bytes(string):
+    if isinstance(string, six.binary_type):
+        return string
+    else:
+        return string.encode('UTF-8')

barbican/tests/plugin/crypto/test_pkcs11.py

@@ -399,3 +399,9 @@ class WhenTestingPKCS11(utils.BaseTestCase):
     def test_check_error_with_token_error(self):
         self.assertRaises(exception.P11CryptoTokenException,
                           self.pkcs11._check_error, 0xe0)
+
+    def test_converting_unicode_to_bytes(self):
+        self.assertEqual(b'foo', pkcs11._to_bytes(u'foo'))
+
+    def test_converting_default_str_type_to_bytes(self):
+        self.assertEqual(b'foo', pkcs11._to_bytes('foo'))