SSO from custom application to SharePoint 2010

Question

I have a custom web application that authenticates against Active Directory. I need to provide single sign on from my application TO SharePoint.

There are plenty of resources describing how to authenticate from sharepoint to a custom application, but I have not found any describing authentication from an external system to sharepoint where both applications authenticate against the same domain.

Use case
1. User logs into my application via form
2. User clicks link to sharepoint
3. New window opens and user is logged into sharepoint

What options do I have? I have read about Secure Store Services (SSS), but it appears that this is for authenticating a user between 2 separate user bases. Both my application and sharepoint will be using Active Directory for authentication.

Answer 1

Maybe this will help:
http://social.msdn.microsoft.com/Forums/en-US/sharepointdevelopment/thread/f77d03bd-5cab-48bd-b16e-aaec809c24c7

Another links:
http://www.usingnat.net/sharepoint/2011/2/23/how-to-programmatically-authenticate-to-uag-protected-sharep.html
http://blackninjasoftware.com/2009/04/09/how-to-programmatically-impersonate-users-in-sharepoint/
http://social.msdn.microsoft.com/forums/en-US/sharepointdevelopment/thread/00a41275-bdb3-4987-b7f7-1b0fc265cb3e