same application, multiple custumers (of which each one has it's own database)

[eluser]CI beyond[/eluser]
each customer is a company with numerous users I'd rather avoid writing extra stuff for authentication and redirecting. I'm simply looking for a way to put all these redundant sources in 1 place and somehow still manage to connect to the corrct database.

To be clear: company A could have users named 1, 2 and 3, while company B could also have users named 1, 2 and 3. Even if i would write some central database this would require the users to select from which company they're from which is not only inconvenient but also not very sensitive in light of privacy

I was more thinking along the lines of some smart symlinking on the webserver.