code: public static SingleSignonToken getSSOToken(Subject subject) {
          SingleSignonToken ssoToken = null;
          Set<SingleSignonToken> ssoTokens = subject.getPrivateCredentials(SingleSignonToken.class);
          Iterator<SingleSignonToken> ssoTokensIterator = ssoTokens.iterator();
          if (ssoTokensIterator.hasNext()) {
              ssoToken = ssoTokensIterator.next();
          }
          return ssoToken;
      }
docs: Gets the SSO token from the subject.
  
  @param subject {@code null} is not supported.
  @return