Dynamic initial value for the username using forms and views from django.contrib.auth

I am presently using the login view and the AuthenticationForm from django.contrib.auth.views to login users.

Now, I would like to extend this solution to prepopulate the username field from the request object (I can infer the username if visitors are authenticated elsewhere). Because I am lazy and would like to keep dry, I wonder if this is possible without replicating the entire login view code.

I am aware of dynamic initial values in Django, but I cannot see how these might be passed into the login view (which does not accept form instances as parameter).

On the IRC channel, it was suggested that I extend the AuthenticationForm to process the request, however (as far as I understand), the reque开发者_如何学运维st is not always passed on to the form (rather only when the form is submitted, which would be too late).

The only alternative I can think of is writing a custom login view to add initial values, which would basically replicate the code from the contrib.auth package (plus passing initial values to the form).

My question, then, is this: Is there a simpler alternative, one that would get by without copying code? Any hints would be much appreciated. Thanks!

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The request is passed into the form on GET - see line 54 of django.contrib.auth.views. So yes, extending the form to take the username seems like the best way to go. Something like (untested):

class ExtendedAuthForm(AuthenticationForm):
    def __init__(self, request=None, *args, **kwargs):
        if request is not None:
            username = request.get_username_however()
            initial = kwargs.get('initial', {})
            initial_default = {'username': username}
            initial_default.update(initial)
            kwargs['initial'] = initial_default
        super(ExtendedAuthForm, self).__init__(request, *args, **kwargs)