Fix AuthenticationClient for encrypted channels

The function generate_shared_secret expects the first argument "channel" in binary for Python 3, but it was passed as a string. That caused a `TypeError: can only concatenate str (not "bytes") to str` exception when using `authenticate` with encryption.

Author: ericmarcos

pusher/authentication_client.py

@@ -17,6 +17,7 @@
 
 from pusher.util import (
     ensure_text,
+    ensure_binary,
     validate_channel,
     validate_socket_id,
     channel_name_re
@@ -76,7 +77,8 @@ def authenticate(self, channel, socket_id, custom_data=None):
         response_payload = { "auth": auth }
 
         if is_encrypted_channel(channel):
-            shared_secret = generate_shared_secret(channel, self._encryption_master_key)
+            shared_secret = generate_shared_secret(
+                ensure_binary(channel, "channel"), self._encryption_master_key)
             shared_secret_b64 = base64.b64encode(shared_secret)
             response_payload["shared_secret"] = shared_secret_b64