It must be a fairly standard wheel, so I'd rather not reinvent it.

Create/modify/delete users. Ditto their passwords & maybe enforce password change every X days. Also, create groups, like "sales", "support", etc and add/remove users.

The only unique part should be what they have permission to do (visit certain parts of the site after login, etc)

And I'd like to store admin data in an ODBC compliant database (MySql to start with, but I may move on).

Is this a new wheel?

There doesn't seem to be much of anything on SourceForge, but if I could find something established and trusted I wouldn't even mind paying a few $100 as a trade of for the time needed to develop & test it.