How do I setup single sign on in ASP.NET

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C#

ASP.NET

SQL-Server-2008R2

We have three different applications running on ASP.Net 4.0 and SQLServer 2008, the username/password etc to these applications are stored in user tables in the respective database separately (not forms/windows authentication). An user may have access to all three applications or only one. Currently if the user has access to all applications he has to login separately to each application, logout and login again to another application. Our boss wants make it as a single login page where the user can login and depending on the privilege he has the respective application icons should be shown, when he logout from that application without login again he should be able to access the other application. My issue is currently when user login separately to the application few session parameters are passed. When I write a wrapper for common login how do I maintain these session parameters. Also is it possible to maintain session timeout All three applications are in different sub domains in same server. Please advise. Thanks in advance.

What I have tried:

I created a common table which will has all loginid and passwords from three applications, and created a wrapper application in which the credentials are captured. First the username will be checked in the common login table and depending on the application access he has, the respective database and application should be invoked.I am able to get the details of the access for the user. How can I pass the required session parameters to each applications from the respective user tables to invoke the respective applications.