code: public Subject login(Subject subject) throws MessagingAuthenticationException {
  		if (TraceComponent.isAnyTracingEnabled() && tc.isEntryEnabled()) {
  			SibTr.entry(tc, CLASS_NAME + "login", subject);
  		}
  		Subject result = null;
  		if (!runtimeSecurityService.isMessagingSecure()) {
  			result = runtimeSecurityService.createUnauthenticatedSubject();
  		} else {
  			if (messagingAuthenticationService != null) {
  				result = messagingAuthenticationService.login(subject);
  			}
  		}
  		if (TraceComponent.isAnyTracingEnabled() && tc.isEntryEnabled()) {
  			SibTr.exit(tc, CLASS_NAME + "login", result);
  		}
  		return result;
  	}
docs: Login method to authenticate based on the Subject
  <ul>
  <li>If Security is enabled, it calls the MessagingAuthenticationService
  for authenticating</li>
  <li>If Security is disabled, it returns a Unauthenticated Subject</li>
  </ul>
  
  @param subject
  The Subject (mostly already authenticated) passed from
  authorization code
  @return subject - If User is authenticated null - If User is
  unauthenticated