How to make SSO, Single Sign-On in ASP.NET for two sub domains?

1. Put same machine keys setting in two web.config file:
http://rayaspnet.blogspot.com/2011/11/how-to-generate-machine-key-for-aspnet.html

2. Modify following parts in two web.config files:
Name, domain, path and enableCrossAppRedirects

<authentication mode="Forms">
  <forms name=".ASPNET" path="/" domain="abc.com" enableCrossAppRedirects="true" />
</authentication>