Raise an exception when the oauth flow fails

Author: mafrosis

gcsa/_services/authentication.py

@@ -9,6 +9,8 @@
 from google.auth.transport.requests import Request
 from google.auth.credentials import Credentials
 
+from gcsa.exceptions import FailedToAuthenticateError
+
 
 class AuthenticatedService:
     """Handles authentication of the `GoogleCalendar`"""
@@ -123,6 +125,9 @@ def _get_credentials(
                 except WSGITimeout:
                     print('Authentication flow timed out. Please try again.')
 
+            if credentials is None:
+                raise FailedToAuthenticateError
+
             if save_token:
                 with open(token_path, 'wb') as token_file:
                     pickle.dump(credentials, token_file)

gcsa/exceptions.py

@@ -0,0 +1,2 @@
+class FailedToAuthenticateError(Exception):
+    'Failed to authenticate to the Google API'