fix(socialaccount): Remove hard-coded redirect URL

[c-w]

This pull request moves all uses of reverse("socialaccount_connections") into the social account adapter so that they can be consistently overwritten in just one place. There was already a helper method for to format the redirect URL, but it wasn't used in all edge cases.

Besides increasing code consistency, the changes in this pull request also fix using django-allauth in combination with dj-rest-auth in the scenario where we have an existing account for a new social login. Previously, we would experience a crash unless a dummy URL is configured for socialaccount_connections. After the fix in this PR is merged, instead of setting this dummy URL we can now override the redirect URL in the adapter which is much cleaner.

[coveralls]

Coverage: 91.767% (-0.007%) from 91.774% when pulling 8b98127 on c-w:remove-hard-coded-redirect into 99b67e8 on pennersr:master.

[pennersr]

Question: Why is this assert being removed? Same question for the one below.

[c-w]

If this PR is merged, get_connect_redirect_url will be used in both branches of the if request.user.is_anonymous conditional so I moved the assertion out of the adapter method and into the call site as otherwise calling the adapter method in the the true branch of that conditional would always raise an exception.

Maybe the above explanation isn't super clear so let me annotate some code to help explain my rationale:

if request.user.is_anonymous:
    # this will raise an exception on `assert request.user.is_authenticated`
    # so we need to remove the assertion from the adapter
    connect_redirect_url = get_adapter(request).get_connect_redirect_url(request, sociallogin.account)
    return HttpResponseRedirect(connect_redirect_url)
#
# ... some code omitted for brevity ...
#
# this will not raise on exception on `assert request.user.is_authenticated`
# so for backwards compatibility we can move the assertion from the adapter
# to just before the call site here
assert request.user.is_authenticated
default_next = get_adapter(request).get_connect_redirect_url(request, sociallogin.account)

[c-w]

Thanks for the merge 🎉