code: protected Principal getPrincipal() {
          final Object principal = requestContext.getProperty("Principal");
          if (principal != null) {
              return (Principal) principal;
          } else {
              return null;
          }
      }
docs: Returns the principal for who initiated the request.
  @return a Principal object
  @see alpine.model.ApiKey
  @see alpine.model.LdapUser
  @since 1.0.0