In this scenario, the customer requires that users do not directly access websites and that a security device (the firewall) manages the connection, while also ensuring that there is authentication back to the Active Directory (AD) servers for all sessions. The explicit proxy with Kerberos authentication is the best solution because:

The explicit proxy allows the firewall to intercept user web traffic and manage the connections on behalf of users.

Kerberos authentication ensures that the user’s identity is validated against the Active Directory servers before the session is allowed, fulfilling the authentication requirement.