There are four ways of Authentication options available in SERVLETS
HTTP basic authentication
In this, server uses the username and password provided by the client and these credentials are TRANSMITTED using simple base64 encoding.
HTTP digest authentication
This option is same the basic authentication except the password is encrypted and transmitted using SHA or MD5.
HTTPS client authentication
This options is based on HTTP over SSL.
Form-based authentication
Form-based authentication uses login page to COLLECT username and password.

There are four ways of Authentication options available in servlets
HTTP basic authentication
In this, server uses the username and password provided by the client and these credentials are transmitted using simple base64 encoding.
HTTP digest authentication
This option is same the basic authentication except the password is encrypted and transmitted using SHA or MD5.
HTTPS client authentication
This options is based on HTTP over SSL.
Form-based authentication
Form-based authentication uses login page to collect username and password.