Single Login page for multiple applications.

Hi,
 
I was developed 4 applications with different login pages by using "asp.net web site administration tool 2010" and i deployed in server(IIS).
Now the requirement is like i need to create new application with common login page and home page for 4 applications. By using that common home page i need to access 4 aplications which i deployed in iis.
 
Thank you.