Passing information from passdb to userdb

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I'm trying to hack together a new authentication back-end and I wanted to know if it's possible to pass values from passdb to userdb in the auth_request structure at authentication time. I modified struct auth_request in auth-request.h to contain a new variable and it gets set properly in my passdb, however the value is not there when checking for it userdb.
I'm very novice when it comes to Dovecot programming so any help is appreciated.
Thanks!