Tuesday, 3 April 2012

Java Authentication and Authorization Service JAAS - Java Security- Create a Login


How to create a custom Jaas Login Module?

Java Authentication and Authorization service allows applications to authenticate subjects independant of the underlying authentication mechanism. This is done by standard interfaces defined in the JAAS architecture. Any authentication mechanism that, conforms to these interfaces can be used by the application through JAAS without getting entangled in the fine details of the mechanism. This is typically used when applications need to authenticate subjects using a different mechanism than provided as part of an application framework. For example, custom database lookup to autheticate users rather than FORM authentication in a webapp under tomcat.

The LoginContext allows applications to login and out i.e authenticate(and also authorize). Applications don't interact with the security mechanism that provides the authentication mechanism. It may be a kerberos login or a login mechanism where you deal the user name and password. When you initialise the context you specify the LoginModule_Configuration you will use to login. You also specify the callback handlers which gets the information from the user(or someother place) and puts it in callbacks. Callback has the info needed by application. Callbackhandler implements interfaces which allow the application classes to get the information from the authentication mechanism. While the application is executing the login() method of the underlying
authentication mechanism, the handlers get the credentials and puts them in the callback. In the login() method the call backs can be polled to get the information they have.

Handler's handle method sample.
Login method in a class that extends LoginModule interface.

Loginmodule is an implementation of the jaas compatible security mechanism that, performs the authentication. A custome module can be coded by implementing the interface.The modules available are specified in a jaas configuration file and that module classes/jars should be available for the application to load.

Jaas configuration file.


You mention the options to be used with a loginmodule in the jaas configuration file. For example, do you want the loginmodule to be a mandatory success thing for applications to go through? requisite? failing ok? you mention the location of the jaas configuration file in  your java.security file. The java.security file is located in your_jre/lib/security/java.security. This is underlying login.config.url.= your_jaas_config_file here. if nothing is mentioned here it will look in you home folder for .java.login.config file. Sometimes a
behaviour noted is that, if you are running as a root user this will be accessed irrespective of anything else!!. This is the case when you run from eclipse as a root user. Simply put, this is the name of the class that implements the LoginModule interface. Standard providers like kerberos do this. You can also implement the
interface and put it here. The name at the top of the {} brackets is the 'name of the login configuration' you will refer to in your application.

Example jaas configuration specification in Java.Security file

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