Configure LMS to select oauth2 providing library.

Available backends:

* django-oauth-toolkit (DOT)
* django-oauth2-provider (DOP)

* Use provided client ID to select backend for
  * AccessToken requests
  * third party auth-token exchange
* Create adapters to isolate library-dependent functionality
* Handle django-oauth-toolkit tokens in edX DRF authenticator class

MA-1998
MA-2000

lms/djangoapps/oauth_dispatch/views.py

@@ -0,0 +1,89 @@
+"""
+Views that dispatch processing of OAuth requests to django-oauth2-provider or
+django-oauth-toolkit as appropriate.
+"""
+
+from __future__ import unicode_literals
+
+from django.views.generic import View
+from edx_oauth2_provider import views as dop_views  # django-oauth2-provider views
+from oauth2_provider import models as dot_models, views as dot_views  # django-oauth-toolkit
+
+from auth_exchange import views as auth_exchange_views
+
+from . import adapters
+
+
+class _DispatchingView(View):
+    """
+    Base class that route views to the appropriate provider view.  The default
+    behavior routes based on client_id, but this can be overridden by redefining
+    `select_backend()` if particular views need different behavior.
+    """
+    # pylint: disable=no-member
+
+    dot_adapter = adapters.DOTAdapter()
+    dop_adapter = adapters.DOPAdapter()
+
+    def dispatch(self, request, *args, **kwargs):
+        """
+        Dispatch the request to the selected backend's view.
+        """
+        backend = self.select_backend(request)
+        view = self.get_view_for_backend(backend)
+        return view(request, *args, **kwargs)
+
+    def select_backend(self, request):
+        """
+        Given a request that specifies an oauth `client_id`, return the adapter
+        for the appropriate OAuth handling library.  If the client_id is found
+        in a django-oauth-toolkit (DOT) Application, use the DOT adapter,
+        otherwise use the django-oauth2-provider (DOP) adapter, and allow the
+        calls to fail normally if the client does not exist.
+        """
+
+        if dot_models.Application.objects.filter(client_id=self._get_client_id(request)).exists():
+            return self.dot_adapter.backend
+        else:
+            return self.dop_adapter.backend
+
+    def get_view_for_backend(self, backend):
+        """
+        Return the appropriate view from the requested backend.
+        """
+        if backend == self.dot_adapter.backend:
+            return self.dot_view.as_view()
+        elif backend == self.dop_adapter.backend:
+            return self.dop_view.as_view()
+        else:
+            raise KeyError('Failed to dispatch view. Invalid backend {}'.format(backend))
+
+    def _get_client_id(self, request):
+        """
+        Return the client_id from the provided request
+        """
+        return request.POST.get('client_id')
+
+
+class AccessTokenView(_DispatchingView):
+    """
+    Handle access token requests.
+    """
+    dot_view = dot_views.TokenView
+    dop_view = dop_views.AccessTokenView
+
+
+class AuthorizationView(_DispatchingView):
+    """
+    Part of the authorization flow.
+    """
+    dop_view = dop_views.Capture
+    dot_view = dot_views.AuthorizationView
+
+
+class AccessTokenExchangeView(_DispatchingView):
+    """
+    Exchange a third party auth token.
+    """
+    dop_view = auth_exchange_views.DOPAccessTokenExchangeView
+    dot_view = auth_exchange_views.DOTAccessTokenExchangeView