code: public void enableKerberosAuthentication(final String loginContextEntryKey) {
         try {
             LoginContext lc = new LoginContext(loginContextEntryKey);
             lc.login();
             m_subject = lc.getSubject();
         } catch (SecurityException | LoginException ex) {
             throw new IllegalArgumentException("Cannot determine client consumer's credentials", ex);
         }
      }
docs: <p>Use the provided JAAS login context entry key to get the authentication
  credentials held by the caller<p>
  
  @param loginContextEntryKey JAAS login context config entry designation