The current auth backend code catches TypeError to detect backends that
do not support specified argumetnts. As a result, any TypeErrors raised
within the actual backend code are silenced.
In Python 2.7+ and 3.2+ this can be avoided by using inspect.getcallargs().
With this method, we can test whether arguments match the signature without
actually calling the function.
Thanks David Eyk for the report.
Removing a backend configured in AUTHENTICATION_BACKENDS should not
raise an exception for existing sessions, but should make already
logged-in users disconnect.
Thanks Bradley Ayers for the report.
Michał Górny
Aymeric Augustin
Jorge Bastida
Preston Timmons