code: public String getPrincipal() {
          String[] accessIDArray = getAttributes("u");
  
          if (accessIDArray != null && accessIDArray.length > 0)
              return accessIDArray[0];
          else
              return null;
      }
docs: Gets the principal that this Token belongs to. If this is an authorization token,
  this principal string must match the authentication token principal string or the
  message will be rejected.
  
  @return String