A Configuration object is responsible for specifying which LoginModules should be used for a particular application, and in what order the LoginModules should be invoked.

  A Configuration object is responsible for specifying which LoginModules should be used for a particular application, and in what order the LoginModules should be invoked.

A login configuration contains the following information. Note that this example only represents the default syntax for the Configuration. Subclass implementations of this class may implement alternative syntaxes and may retrieve the Configuration from any source such as files, databases, or servers.

      Name {
              ModuleClass  Flag    ModuleOptions;
              ModuleClass  Flag    ModuleOptions;
              ModuleClass  Flag    ModuleOptions;
      };
      Name {
              ModuleClass  Flag    ModuleOptions;
              ModuleClass  Flag    ModuleOptions;
      };
      other {
              ModuleClass  Flag    ModuleOptions;
              ModuleClass  Flag    ModuleOptions;
      };
 

Each entry in the Configuration is indexed via an application name, Name, and contains a list of LoginModules configured for that application. Each LoginModule is specified via its fully qualified class name. Authentication proceeds down the module list in the exact order specified. If an application does not have specific entry, it defaults to the specific entry for "other".

The Flag value controls the overall behavior as authentication proceeds down the stack. The following represents a description of the valid values for Flag and their respective semantics:

      1) Required     - The LoginModule is required to succeed.
                        If it succeeds or fails, authentication still continues
                        to proceed down the LoginModule list.

      2) Requisite    - The LoginModule is required to succeed.
                        If it succeeds, authentication continues down the
                        LoginModule list.  If it fails,
                        control immediately returns to the application
                        (authentication does not proceed down the
                        LoginModule list).

      3) Sufficient   - The LoginModule is not required to
                        succeed.  If it does succeed, control immediately
                        returns to the application (authentication does not
                        proceed down the LoginModule list).
                        If it fails, authentication continues down the
                        LoginModule list.

      4) Optional     - The LoginModule is not required to
                        succeed.  If it succeeds or fails,
                        authentication still continues to proceed down the
                        LoginModule list.
 

The overall authentication succeeds only if all Required and Requisite LoginModules succeed. If a Sufficient LoginModule is configured and succeeds, then only the Required and Requisite LoginModules prior to that Sufficient LoginModule need to have succeeded for the overall authentication to succeed. If no Required or Requisite LoginModules are configured for an application, then at least one Sufficient or Optional LoginModule must succeed.

ModuleOptions is a space separated list of LoginModule-specific values which are passed directly to the underlying LoginModules. Options are defined by the LoginModule itself, and control the behavior within it. For example, a LoginModule may define options to support debugging/testing capabilities. The correct way to specify options in the Configuration is by using the following key-value pairing: debug="true". The key and value should be separated by an 'equals' symbol, and the value should be surrounded by double quotes. If a String in the form, MISSING_VALUE !, occurs in the value, it will be expanded to the value of the system property. Note that there is no limit to the number of options a LoginModule may define.

The following represents an example Configuration entry based on the syntax above:

 Login {
   com.sun.security.auth.module.UnixLoginModule required;
   com.sun.security.auth.module.Krb5LoginModule optional
                   useTicketCache="true"
                   ticketCache="MISSING_VALUE !${/}tickets";
 };
 

This Configuration specifies that an application named, "Login", requires users to first authenticate to the com.sun.security.auth.module.UnixLoginModule, which is required to succeed. Even if the UnixLoginModule authentication fails, the com.sun.security.auth.module.Krb5LoginModule still gets invoked. This helps hide the source of failure. Since the Krb5LoginModule is Optional, the overall authentication succeeds only if the UnixLoginModule (Required) succeeds.

Also note that the LoginModule-specific options, useTicketCache="true" and ticketCache=MISSING_VALUE !${/}tickets", are passed to the Krb5LoginModule. These options instruct the Krb5LoginModule to use the ticket cache at the specified location. The system properties, user.home and / (file.separator), are expanded to their respective values.

There is only one Configuration object installed in the runtime at any given time. A Configuration object can be installed by calling the setConfiguration method. The installed Configuration object can be obtained by calling the getConfiguration method.

If no Configuration object has been installed in the runtime, a call to getConfiguration installs an instance of the default Configuration implementation (a default subclass implementation of this abstract class). The default Configuration implementation can be changed by setting the value of the "login.configuration.provider" security property (in the Java security properties file) to the fully qualified name of the desired Configuration subclass implementation. The Java security properties file is located in the file named <JAVA_HOME>/lib/security/java.security. <JAVA_HOME> refers to the value of the java.home system property, and specifies the directory where the JRE is installed.

Application code can directly subclass Configuration to provide a custom implementation. In addition, an instance of a Configuration object can be constructed by invoking one of the getInstance factory methods with a standard type. The default policy type is "JavaLoginConfig". See Appendix A in the Java Cryptography Architecture API Specification & Reference for a list of standard Configuration types.