ce of calls made to the methods of this interface for the purpose of completing
 a secure message exchange.</dd>
<dd><code>clientSubject</code> - A Subject that represents the source of the service request. It is used by the method
 implementation to store Principals and credentials validated in the request.</dd>
<dd><code>serviceSubject</code> - A Subject that represents the recipient of the service request, or null. It may be used by the
 method implementation as the source of Principals or credentials to