This package presents a framework that allows application developers to make use of security services like authentication, data integrity and data confidentiality from a variety of underlying security mechanisms like Kerberos, using a unified API. The security mechanisms that an application can chose to use are identified with unique object identifiers. One example of such a mechanism is the Kerberos v5 GSS-API mechanism (object identifier 1.2.840.113554.1.2.2). This mechanism is available through the default instance of the GSSManager class.

The GSS-API is defined in a language independent way in RFC 2743. The Java language bindings are defined in RFC 2853

An application starts out by instantiating a `GSSManager` which then serves as a factory for a security context. An application can use specific principal names and credentials that are also created using the GSSManager; or it can instantiate a context with system defaults. It then goes through a context establishment loop. Once a context is established with the peer, authentication is complete. Data protection such as integrity and confidentiality can then be obtained from this context.

The GSS-API does not perform any communication with the peer. It merely produces tokens that the application must somehow transport to the other end.

### Credential Acquisition

The GSS-API itself does not dictate how an underlying mechanism obtains the credentials that are needed for authentication. It is assumed that prior to calling the GSS-API, these credentials are obtained and stored in a location that the mechanism provider is aware of. However, the default model in the Java platform will be that mechanism providers must obtain credentials only from the private or public credential sets associated with the {@link javax.security.auth.Subject Subject} in the current access control context. The Kerberos v5 mechanism will search for the required INITIATE and ACCEPT credentials ({@link javax.security.auth.kerberos.KerberosTicket KerberosTicket} and {@link javax.security.auth.kerberos.KerberosKey KerberosKey}) in the private credential set where as some other mechanism might look in the public set or in both. If the desired credential is not present in the appropriate sets of the current Subject, the GSS-API call must fail.

This model has the advantage that credential management is simple and predictable from the applications point of view. An application, given the right permissions, can purge the credentials in the Subject or renew them using standard Java API's. If it purged the credentials, it would be sure that the JGSS mechanism would fail, or if it renewed a time based credential it would be sure that a JGSS mechanism would succeed.

This model does require that a {@link javax.security.auth.login JAAS login} be performed in order to authenticate and populate a Subject that the JGSS mechanism can later utilize. However, applications have the ability to relax this restriction by means of a system property: `javax.security.auth.useSubjectCredsOnly`. By default this system property will be assumed to be `true` (even when it is unset) indicating that providers must only use the credentials that are present in the current Subject. However, if this property is explicitly set to false by the application, then it indicates that the provider is free to use any credentials cache of its choice. Such a credential cache might be a disk cache, an in-memory cache, or even just the current Subject itself.

## Related Documentation

For an online tutorial on using Java GSS-API, please see {@extLink security_guide_jgss_tutorial Introduction to JAAS and Java GSS-API}.

@since 1.4