[web2py] help configuring model with db.user_auth external key

[monotasker]

Hi. I'm trying to create a table in a model that users db.user_auth as
an external key in one of the fields. But whenever I add db.auth to
the table definition it generates a "key" error compaining about
"user_auth".

Here's the section of the model that throws the error:

db.define_table('question_records',
    Field('user', db.user_auth),
    Field('question', db.questions),
    Field('last_right', 'date', default=request.now),
    Field('last_wrong', 'date', default=request.now),
    Field('times_right'),
    Field('times_wrong'),
    Field('category')
    )

Any idea why this isn't working?

Thanks