sanitize_redirect don't work with Django's reverse_lazy

[volrath]

Hello,

There's an issue when working with Django and setting some of the SOCIAL_AUTH_*_URL to reverse_lazy proxies. The problem is caused in two functions:

sanitize_redirect: Does a quick check first where ask if the given redirect_to is a True-able value and if it's instance of a string type (six.string_types). The problem here is that reverse_lazy returns a Django proxy (reverse_lazy ~= lazy(reverse, str)) and this is not validated by this first check, hence returning None.

do_complete: Here we call sanitize_redirect if the settings say so, but there's no checking if sanitize_redirect returns None. So, if this is the case, a misleading Exception is raised ('NoneType' object has no attribute 'find') since url is set to None and after that, somewhere in the way, a url.find(...) is called.

I forked the project to provided solutions. For sanitize_redirect I'm using the str.decode method to force a reverse_lazy string to get evaluated. This was suggested as one of the solutions for this ticket: https://code.djangoproject.com/ticket/18776 The actual solution is better but is very django-dependent.

For do_complete I'm just adding the extra check after calling sanitize_redirect, maybe that check can be set in a lower indentation level.

Hope this helps.

[omab]

Thanks!