title: django-allauth gives 403 forbidden at callback
body: <p>I am creating a custom provider to get oauth2 tokens from another internal project, the process is almost fine, but I am getting <code>403 forbidden</code> error when browser returns to my project with this url:</p>
  
  <pre><code>http://localhost:8001/account/connect/login/callback/?state=Nngd5Gu3JnB4&amp;code=Rqqg91oEwQKDsvSyzZ8Az5fEeHGaEe#_=_
  </code></pre>
  
  <p>here is the views.py in my custom provider:</p>
  
  <pre><code>import requests
  from allauth.socialaccount.providers.oauth2.views import (OAuth2Adapter, OAuth2LoginView, OAuth2CallbackView)
  from .provider import ConnectProvider
  
  
  class ConnectOAuth2Adapter(OAuth2Adapter):
      provider_id = ConnectProvider.id
      access_token_url = 'http://localhost:8000/o/token/'
      authorize_url = 'http://localhost:8000/o/authorize/'
      profile_url = 'http://localhost:8000/api/account/'
  
      def complete_login(self, request, app, token, **kwargs):
          _token = {'access_token':token.token}
          resp = requests.get(self.profile_url, params={'access_token': token.token, 'alt': 'json'})
          extra_data = resp.json()
          login = self.get_provider().sociallogin_from_response(request, extra_data)
          return login
  
  oauth2_login = OAuth2LoginView.adapter_view(GoConnectOAuth2Adapter)
  oauth2_callback = OAuth2CallbackView.adapter_view(GoConnectOAuth2Adapter)
  </code></pre>