An application client can use the Java Authentication and Authorization Service (JAAS) to create login modules for authentication. A JAAS-based application implements the javax.security.auth.callback.CallbackHandler interface so that it can interact with users to enter specific authentication data, such as user names or passwords, or to display error and warning messages.
Applications implement the CallbackHandler interface and pass it to the login context, which forwards it directly to the underlying login modules. A login module uses the callback handler both to gather input (such as a password or smart card PIN) from users and to supply information (such as status information) to users. Because the application specifies the callback handler, an underlying login module can remain independent of the various ways that applications interact with users.
For example, the implementation of a callback handler for a GUI application might display a window to solicit user input. Or the implementation of a callback handler for a command-line tool might simply prompt the user for input directly from the command line.
The login module passes an array of appropriate callbacks to the callback handler’s handle method (for example, a NameCallback for the user name and a PasswordCallback for the password); the callback handler performs the requested user interaction and sets appropriate values in the callbacks. For example, to process a NameCallback, the CallbackHandler might prompt for a name, retrieve the value from the user, and call the setName method of the NameCallback to store the name.
Java Authentication and Authorization Service (JAAS) in Java Platform, Standard Edition
Java Authentication and Authorization Service (JAAS) Reference Guide
Java Authentication and Authorization Service (JAAS): LoginModule Developer’s Guide
Links to this information are provided in Further Information about Security.