@Override
    public Principal getPrincipal() {
        return null;
    }
@author Marc-Antoine Garrigue
@author Arnaud Lesueur
@author Sven Rieckhoff
@since 5.2.0
support/cas-server-support-spnego/src/test/java/org/apereo/cas/support/spnego/MockUnsuccessfulJcifsAuthentication.java