Share authentication between two Askbot instances

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Hi, I'm currently running an Askbot instance (the classical way: questions and answers) on a subdomain of a website.
I'd like to add another subdomain with another Askbot instance for a kind of gallery (my goal cannot be reached with tags in the first instance), but I'd like my users to be able to sign in only once. So is there a way to make two instances share auth?

I'm totally new at Django, so I don't even know if this page would be of any help:
http://askbot.org/doc/askbot-as-reusable-django-application.html
Can askbot be a sub application of itself?

Thanks reading.