docs: public static String getUniqueUserName(Subject subject) throws MessagingSecurityException {
          if (TraceComponent.isAnyTracingEnabled() && tc.isEntryEnabled()) {
              SibTr.entry(tc, CLASS_NAME + "getUniqueUserName", subject);
          }
          if (subject == null) {
              return null;
          }
  
          WSCredential cred = subjectHelper.getWSCredential(subject);
          String userName = null;
          if (cred != null) {
              try {
                  userName = cred.getSecurityName();
              } catch (CredentialException ce) {
                  throw new MessagingSecurityException(ce);
              } catch (CredentialDestroyedException e) {
                  throw new MessagingSecurityException(e);
              }
          }
          if (TraceComponent.isAnyTracingEnabled() && tc.isEntryEnabled()) {
              SibTr.exit(tc, CLASS_NAME + "getUniqueUserName", userName);
          }
          return userName;
      }