Facebook login cannot get access_token from given code

[koztay]

I am getting the foolowing error when I make a POST request to the rest-auth/registration/facebook/ end-point:

Traceback (most recent call last):
  File "/usr/local/lib/python3.6/site-packages/django/contrib/staticfiles/handlers.py", line 65, in __call__
    return self.application(environ, start_response)
  File "/usr/local/lib/python3.6/site-packages/django/core/handlers/wsgi.py", line 141, in __call__
    response = self.get_response(request)
  File "/usr/local/lib/python3.6/site-packages/django/core/handlers/base.py", line 75, in get_response
    response = self._middleware_chain(request)
  File "/usr/local/lib/python3.6/site-packages/django/core/handlers/exception.py", line 36, in inner
    response = response_for_exception(request, exc)
  File "/usr/local/lib/python3.6/site-packages/django/core/handlers/exception.py", line 90, in response_for_exception
    response = handle_uncaught_exception(request, get_resolver(get_urlconf()), sys.exc_info())
  File "/usr/local/lib/python3.6/site-packages/django/core/handlers/exception.py", line 125, in handle_uncaught_exception
    return debug.technical_500_response(request, *exc_info)
  File "/usr/local/lib/python3.6/site-packages/django_extensions/management/technical_response.py", line 37, in null_technical_500_response
    six.reraise(exc_type, exc_value, tb)
  File "/usr/local/lib/python3.6/site-packages/six.py", line 695, in reraise
    raise value.with_traceback(tb)
  File "/usr/local/lib/python3.6/site-packages/django/core/handlers/exception.py", line 34, in inner
    response = get_response(request)
  File "/usr/local/lib/python3.6/site-packages/django/core/handlers/base.py", line 115, in _get_response
    response = self.process_exception_by_middleware(e, request)
  File "/usr/local/lib/python3.6/site-packages/django/core/handlers/base.py", line 113, in _get_response
    response = wrapped_callback(request, *callback_args, **callback_kwargs)
  File "/usr/local/lib/python3.6/contextlib.py", line 52, in inner
    return func(*args, **kwds)
  File "/usr/local/lib/python3.6/site-packages/django/views/decorators/csrf.py", line 54, in wrapped_view
    return view_func(*args, **kwargs)
  File "/usr/local/lib/python3.6/site-packages/django/views/generic/base.py", line 71, in view
    return self.dispatch(request, *args, **kwargs)
  File "/usr/local/lib/python3.6/site-packages/django/utils/decorators.py", line 45, in _wrapper
    return bound_method(*args, **kwargs)
  File "/usr/local/lib/python3.6/site-packages/django/views/decorators/debug.py", line 76, in sensitive_post_parameters_wrapper
    return view(request, *args, **kwargs)
  File "/usr/local/lib/python3.6/site-packages/rest_auth/views.py", line 49, in dispatch
    return super(LoginView, self).dispatch(*args, **kwargs)
  File "/usr/local/lib/python3.6/site-packages/rest_framework/views.py", line 495, in dispatch
    response = self.handle_exception(exc)
  File "/usr/local/lib/python3.6/site-packages/rest_framework/views.py", line 455, in handle_exception
    self.raise_uncaught_exception(exc)
  File "/usr/local/lib/python3.6/site-packages/rest_framework/views.py", line 492, in dispatch
    response = handler(request, *args, **kwargs)
  File "/usr/local/lib/python3.6/site-packages/rest_auth/views.py", line 103, in post
    self.serializer.is_valid(raise_exception=True)
  File "/usr/local/lib/python3.6/site-packages/rest_framework/serializers.py", line 236, in is_valid
    self._validated_data = self.run_validation(self.initial_data)
  File "/usr/local/lib/python3.6/site-packages/rest_framework/serializers.py", line 437, in run_validation
    value = self.validate(value)
  File "/usr/local/lib/python3.6/site-packages/rest_auth/registration/serializers.py", line 111, in validate
    token = client.get_access_token(code)
  File "/usr/local/lib/python3.6/site-packages/allauth/socialaccount/providers/oauth2/client.py", line 84, in get_access_token
    % resp.content)
allauth.socialaccount.providers.oauth2.client.OAuth2Error: Error retrieving access token: b''

My FacebookLogin view as follows, I installed nginx to serve https in localhost etc. :

class FacebookLogin(SocialLoginView):
    adapter_class = FacebookOAuth2Adapter
    client_class = OAuth2Client
    callback_url = "https://localhost"

The popup window opens and when I give permission to the app, popup windows closes and the HTTP 500 error occurs as the above trace.

[koztay]

I have solved the problem, and the error is not relevant to rest-auth nor allauth. It is relevant to Facebook. The problem was missed backslash for callback_url. In that case Facebook graph api backend gives 500 error without any error messages. It gives just an empty response so, it is not possible to figure out what's going on.