Authenticating against Notes user base

I need to authenticate against our Notes user base and then transfer that information back to be used with an ASP.NET application. Here is the scenerio:

1. User navigates to ASP.NET page
2. Log in
3. Users information is authenticated against Notes and then given proper permissions to the asp.net application based on groups within Notes.

Versions:
Domino R5 5.09 on Windows 2000
ASP.Net 1.0 on Windows 2000 also has MSSQL database it uses for permissions and to hold Web site data.

Is it possible to pass the information into Notes? If so, what do I pass, where do I pass it to and what can I expect to recieve back?

I tried using pop which works, but the Notes administrator does not want to leave pop enabled on the server. Webmail is enabled on the server, so I thought using it some way was the best approach, but I'm not really sure. We are also using a database to re-direct users to their proper mail file "webmaildirect.nsf". It was downloaded from Snadbox or somewhere. I thought it may be possible to use this database if I had a clue where to start.
Microsoft IIS will authenticate using the hhttp://username:password@www.yoursite.com. The other option that should work is using LDAP.

This was first published in October 2002