Allow sensitive_variables() to preserve the signature of its decorated function

[tpazderka]

When the method authenticate of a custom AuthenticationBackend is decorated with sensitive_variables, inspect.getcallargs will always match.

Calling the authenticate function will attempt to call this backend with any set of credentials and will raise an uncaught TypeError for an unmatching backend.

Authentication with such decorated backends used to work in version 1.6.

[Tim Graham]

Could you please try ​bisecting to find the commit where the behavior changed?

[tpazderka]

It is a commit b89c2a5d9eb70ca36629ef657c98e3371e9a5c4f.

[Tim Graham]

Thanks! I'm not sure what can be done to fix this. Any ideas?

[tpazderka]

Nothing apart from going back to the previous masking of TypeError... I think that these two behaviours go against each other...

[Tim Graham]

It might be possible to allow sensitive_variables to preserve the signature of whatever it decorates. Here's code that works until @sensitive_variables is added:

import inspect
from django.views.decorators.debug import sensitive_variables

class Backend(object):
    @sensitive_variables
    def authenticate(self, username=None, password=None):
        print(username)

inspect.getcallargs(Backend().authenticate, username='foo', password='bar')

[Vlastimil Zíma]

What about something like this:

def sensitive_variables(*variables):
    def decorator(func):
        @functools.wraps(func)
        def sensitive_variables_wrapper(*func_args, **func_kwargs):
            ...
        # Keep the original function for inspection in `authenticate`
        sensitive_variables_wrapper.sensitive_variables_func = func
        return sensitive_variables_wrapper
    return decorator

Function authenticate would then check the sensitive_variables_func first.

[Baptiste Mispelon]

I've looked into this and it turns out the issue lies with inspect.getcallargs which doesn't follow the __wrapped__ attribute set by functools.wraps().

Using inspect.signature(...).bind(...) instead of inspect.getcallargs(...) fixes the issue (as an added bonus, getcallargs() has been deprecated since Python 3.5 so removing it is a plus).

​PR here

[Mariusz Felisiak <felisiak.mariusz@…>]

In 3df3c5e6:

Fixed #26480 -- Fixed crash of contrib.auth.authenticate() on decorated authenticate() methods of authentication backends.

The Signature API (PEP 362) has better support for decorated functions
(by default, it follows the wrapped attribute set by
functools.wraps for example).