Application Client-Tier Security - The J2EE 1.4 Tutorial

Application Client-Tier Security

Authentication requirements for J2EE application clients are the same as the requirements for other J2EE components. Access to protected resources in either the EJB tier or the web tier requires user authentication, whereas access to unprotected resources does not.

An application client can use the Java Authentication and Authorization Service (JAAS) for authentication. JAAS implements a Java version of the standard Pluggable Authentication Module (PAM) framework, which permits applications to remain independent of underlying authentication technologies. You can plug new or updated authentication technologies under an application without making any modifications to the application itself. Applications enable the authentication process by instantiating a LoginContext object, which, in turn, references a configuration to determine the authentication technologies or login modules that will be used to perform the authentication.

A typical login module can prompt for and verify a user name and password. Other modules can read and verify a voice or fingerprint sample.

In some cases, a login module must communicate with the user to obtain authentication information. Login modules use a javax.security.auth.callback.CallbackHandler for this purpose. 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 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.

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