Exception will be raised when settings.PASSWORD_HASHERS changes and the check_password() method is called in an asynchronous context.

[Dingning]

When settings.PASSWORD_HASHERS is changed and user.check_password() is called in an async context, a SynchronousOnlyOperation exception may occur.

The reason is that the check_password function will call the synchronous setter function to update the password field of the user table when the settings.PASSWORD_HASHERS is changed.

To reproduce the process:

1. Start Django and create a user. Suppose the user's password is 123456.
2. Close the server, modify settings.PASSWORD_HASHERS, for example, exchange the order of the first two Hashers. You can refer to django.conf.global_settings.PASSWORD_HASHERS.
3. Start the server and call user.check_password('123456') in the asynchronous view.
4. SynchronousOnlyOperation is raiesd.

Reference Code:

from django.http import HttpResponse
from django.contrib.auth import get_user_model


async def test_check_password(request):
    user = await get_user_model().objects.aget(id=1)
    is_correct = user.check_password('123456')

    return HttpResponse(is_correct)

Significance:

1. When settings.PASSWORD_HASHERS changes, check_password and related functions can be called normally in an asynchronous environment.
2. Lay the foundation for the future django.contrib.auth module to support native async.

Solution:

Add acheck_password method, this method will call the async setter function to update the password field of the user table when the settings.PASSWORD_HASHERS is changed.

Demo:

I simply implemented the solution mentioned above and put it here for reference.
​https://github.com/HappyDingning/django/tree/acheck_password

Related discussions:

​https://forum.djangoproject.com/t/add-async-support-for-abstractbaseuser-check-password/20364

Thanks to bigfootjon, carltongibson and UriahKingsley