This is some good reading about access tokens and kerberos from the TechNet “Ask the Directory Services Team” blog.

What’s in a Token

What’s in a Token (Part 2): Impersonation

Kerberos for the Busy Admin

Understanding Kerberos Double Hop

Kerberos Authentication problems – Service Principal Name (SPN) issues - Part 1

Kerberos Authentication problems – Service Principal Name (SPN) issues - Part 2

Kerberos Authentication problems – Service Principal Name (SPN) issues - Part 3