When you deploy an AD FS 2.0 Federation Server farm you must specify a domain-based service account, and the AD FS 2.0 service account needs to have a SPN (servicePrincipalName) registered to allow Kerberosto function for the Federation Service…Reconfiguring the service names in an ADFS Server farm requires hard work.

An ADFS Server farm uses a service account. Whenever you update the URL, the SPN for that service account needs to be updated as well.

There’s a good article from Adam Conkle on TechNet..click here to read more

Thanks Adam and Ed

Enjoy!!