text: Title: Problem with current session API + mfa + social auth
  Body: Hello, I'm seeing unexpected behavior on the current session API. I made a small reproduction repo [here](https://gitlab.com/bufke/allauth-headless-social-mfa). 
  
  It looks like under some circumstances, the current session API is not returning mfa_authenticate after the user authenticates with social auth and needs to proceed to MFA auth. This renders the user unable to login. The same user account works fine, completing both social and MFA auth, using the regular django templates at /accounts/.
  
  The current session api works fine on https://react.demo.allauth.org and when I run a JavaScript dev server that proxies API requests to the backend. I suspect the issue has something to do with stash/unstash_login in [account/utils.py](https://github.com/pennersr/django-allauth/blob/cfd14550ddd4115b4b50b1aca54719cbcbf55f9b/allauth/account/utils.py#L169). 
  
  When it works (in my js dev server), I see unstash gets a <allauth.account.models.Login object at 0x759959adb770> object. But does not when it isn't working (in the pure django example). 
  
  I'll continue to debug but let me know if you have any ideas. I think I've demonstrated the problem in a very trivial JS example above.