KERBEROS - 2
Kerberos is freely available from MIT. It provides the tools of authentication and strong cryptography over the network to help secure information systems across an entire enterprise.
Kerberos is not effective against password guessing attacks;
To be useful, Kerberos must be integrated with other parts of the system.
Kerberos does not itself provide authorization, but V5 Kerberos passes authorization information generated by other services. In this manner, Kerberos can be used as a base for building separate distributed authorization services.