Authentication is the process of identifying the other party to a transaction, and it's the core of Domino security. A server can't usually tell what degree of access to data to permit if it doesn't know the identity of the user. Of course, for some purposes the server doesn't need to know and doesn't bother to authenticate. Also, the degree and type of authentication depend on the kind of client a user employs.
Domino servers and their clients can use four kinds of authentication:
Notes proprietary. This is how Domino servers and Notes clients normally authenticate each other. It is certificate-based and very secure.
Secure Sockets Layer (SSL). This is an optional form of authentication that you can enable for non-Notes ...