Cross app on subdomain form authentication not working

We've been investigating this issue for a week now. We have two applications deployed in two servers. domain.com.cz/app1 sub.domain.com.cz/app2

They do have the same validationKey, decryptionKey, and validation prop开发者_StackOverflow中文版erties in machineKey section.

They also have the same domain in forms authentication, also enableCrossAppRedirects="true" and cookieless="UseCookies".

They have been sharing authentication for years already, but now its not working. As told by sys ads, there were no server config happened prior to the problem.

What other check items should we scan? Thank you.

The first thing to check is whether the cookie is sent to the second subdomain. You could use FireBug for this.

If the cookie is sent there could be various reasons for authentication not working:

• Different versions of the .NET framework (IIRC in .NET 4.0 they changed encryption algorithms)
• Differences in security patches installed? There are some KB patches for .NET that modify the encryption algorithms.