I know this is old but I thought I would answer this for others stumbling across this via google search.

For Single Sign On across platforms you probably want to implement a SAML based solution. SAML stands for Security Assertion Markup Language and is an XML based solution. On the side of things you can use an open source library that makes it easier called SimpleSAMLphp (simplesamlphp.org). 

I'm not sure if the asp.net side of things has an open source library for you to use but since SAML is an open standard you should be able to do it with pure asp.net.

Single Sign On with SubDomains
About: http://stackoverflow.com/review/suggested-edits/1962857

Recently, I've been suggesting a lot of edits - to make the site better. Scrolling through the list of my suggestions, I saw that this was rejected: http://stackoverflow.com/review/suggested-edits/1962857 - mostly with the 


  This edit is too minor; suggested edits should be substantive improvements addressing multiple issues in the post.


reason.

However, if you look at the edit, it is substantial. It clarifies the question, and provides grammar and formatting fixes.

Any help?
