Pass parameter on auto login?

Hi guys

I have a database accessible via IWP. I want to be able to give different groups access to certain records in the database, depending on the referring web page. E.G if a user gets directed to the database from web page 'a', they will only get access to 'a' records.

I can hear you thinking, 'set a variable according to the account they use to log in', but this is the problem, I need to have everyone automatically log in with Guest access.

My workaround (in my head at least, I haven't tried it yet) is to have seperate 'log-in' databases for each group, that the users automatically log-in to, which then transfers them to the main database and sets a variable as "user from group 'a'" or similar.

Does anyone see any problems with this approach or have a better solution?