Which authentication method is valid when connecting to Active Directory?

Kerberos authentication is a valid method for connecting to Active Directory, making it the correct choice. Kerberos is a widely used network authentication protocol that provides secure authentication for users and services within a domain. It is particularly effective in environments where secure, mutual authentication is required, such as when accessing resources in Active Directory.

Active Directory fundamentally relies on Kerberos as its primary authentication protocol because it is designed to prevent eavesdropping and replay attacks. By using ticket-granting tickets (TGTs) and service tickets, Kerberos allows secure communication between users and services without sending plaintext passwords over the network.

While NTLM authentication is also supported by Active Directory, relying exclusively on it would not utilize the advanced security features provided by Kerberos. Basic authentication, on the other hand, is not recommended due to its vulnerability to various attacks since it transmits credentials in an easily decipherable format. Custom proprietary authentication methods could present interoperability issues and are generally not standard for connection to Active Directory environments, which favor well-established protocols like Kerberos.