Django: "settings.DATABASES is improperly configured" upon migrate, but can access database through ORM

Question

I'm having trouble migrating my database and creating authentication tables to my application's database for superusers, staff, etc. which has to be done by performing python manage.py migrate. I believe my problems are occuring because I'm using legacy databases hosted on a Microsoft SQL Server instance, but I'm not sure and I might just have some things set up wrong.

I expect to connect to the database and add an admin/authentication table to an existing database ('authentication_database'), however I receive the following error message:

django.core.exceptions.ImproperlyConfigured: settings.DATABASES is improperly configured. Please supply the ENGINE value. Check settings documentation for more details.

It should be noted that I can access the client_database's ORM via interactive shell/custom management commands. I simply can not migrate the database.

Here is my DATABASES setting in settings.py:

DATABASES = {
    'default': {},
    'auth_db': {
        'NAME': 'authentication_database',
        'HOST': 'host.ip.address.yo',
        'PORT': '',
        'ENGINE': 'sql_server.pyodbc',
        'OPTIONS': {
            'driver': 'SQL Server Native Client 11.0',
        },
    },
    'client_database': {
        'NAME': 'client_database',
        'HOST': 'host.ip.address.yo',
        'PORT': '',
        'ENGINE': 'sql_server.pyodbc',
        'OPTIONS': {
            'driver': 'SQL Server Native Client 11.0',
        },
    },
}

# Database routers
DATABASE_ROUTERS = ['app_name.dbrouter.ClientRouter', 'project_name.authrouter.AuthRouter']

DATABASE_CONNECTION_POOLING = False

I can provide my auth routing code if that could help.

I can also provide a full stack trace if that will help. I just don't currently wish to edit out identifying information in the meantime. Thanks!~