How can I login to django using tastypie

I'm trying to override is_authenticated in my custom authentication. I have something simple (to start with) like this:

class MyAuthentication(BasicAuthentication):
    def __init__(self, *args, **kwargs):
        super(MyAuthentication, self).__init__(*args, **kwargs)

    def is_authenticated(self, request, **kwargs):
        return True

then in my ModelResource I have

class LoginUserResource(ModelResource):

    class Meta:
        resource_name = 'login'
        queryset = User.objects.all()
        excludes = ['id', 'email', 'password', 'is_staff', 'is_superuser']
        list_allowed_methods = ['post']

        authentication = MyAuthentication()
        authorization = DjangoAuthorization()

I keep getting a 500 error back with "error_message": "column username is not unique". I only have one username in the db and it's the user I am trying to authenticate.

Any ideas as to why it's returning this error? How would I allow an api client to login?

Thanks for the help.