Implement Single SignOn in Subdomains in ASP.Net

Hi,

I am planning to have 2 subdmains on my IIS server. Example - www.Portal.MyDomain.Com and www.App.MyDomain.Com. So if someone logs on Portal and if we clicks on the App link, he should be successfuly logged into App.

SO basically 1 signin for both subdomains. Can you advise on how to achive it in ASP.Net 4, C#, VS.Net 2013?

Thanks,

Sanjeev.