Error finishing profile, but works on hard refresh

[njaladan]

NOTE: I could not reproduce this issue. It only happened the first time I logged on, so it may be a fluke? However, it's reproducible on local!

Steps I took:

1. Logged in with Slack for the first time.
2. Filled out the "create my profile" fields, which was basically just my picture and grad year and stuff.
3. Click next, arrive at this error.

How I resolved it:

1. Just went to the main page and connected with Slack again, and it worked this time (automatically logged in and didn't need to fill out any information).

Traceback:

File "/app/.heroku/python/lib/python3.6/site-packages/django/contrib/auth/__init__.py" in login
  111.         backend = backend or user.backend

File "/app/.heroku/python/lib/python3.6/site-packages/django/utils/functional.py" in inner
  214.         return func(self._wrapped, *args)

During handling of the above exception ('AnonymousUser' object has no attribute 'backend'), another exception occurred:

File "/app/.heroku/python/lib/python3.6/site-packages/django/core/handlers/exception.py" in inner
  34.             response = get_response(request)

File "/app/.heroku/python/lib/python3.6/site-packages/django/core/handlers/base.py" in _get_response
  126.                 response = self.process_exception_by_middleware(e, request)

File "/app/.heroku/python/lib/python3.6/site-packages/django/core/handlers/base.py" in _get_response
  124.                 response = wrapped_callback(request, *callback_args, **callback_kwargs)

File "/app/codedoor/views/profiles.py" in finishprofile
  87.         auth_login(request, user)

File "/app/.heroku/python/lib/python3.6/site-packages/django/contrib/auth/__init__.py" in login
  118.                 'You have multiple authentication backends configured and '

Exception Type: ValueError at /codedoor/finishprofile/
Exception Value: You have multiple authentication backends configured and therefore must provide the `backend` argument or set the `backend` attribute on the user.```