code: @Override
    public UserGroupInformation getProxiedUser(final Props userProp)
        throws HadoopSecurityManagerException {
      final String userToProxy = verifySecureProperty(userProp, JobProperties.USER_TO_PROXY);
      final UserGroupInformation user = getProxiedUser(userToProxy);
      if (user == null) {
        throw new HadoopSecurityManagerException(
            "Proxy as any user in unsecured grid is not supported!");
      }
      return user;
    }
docs: Create a proxied user, taking all parameters, including which user to proxy from provided
  Properties.