code: function getAuthentication(authModel, config) {
  
    /**
     * @name authenticate
     * @function
     * @memberOf getAuthentication
     * Authenticate the user.
     * @param {String} name - The name used to authenticate the user
     * @param {String} password - The hashed password
     * @param {function} done - The callback function called with an error or the valid user object
     */
    function authenticate(name, password, done) {
      authModel.findOne({name: name, active: true}, function (err, user) {
        if (err) {
          return done(err);
        }
  
        if (!user) {
          return done(null, false, {message: 'Unknown user'});
        }
  
        if (!user.authenticate(password)) {
          return done(null, false, {message: 'Wrong password'});
        }
  
        return done(null, user);
      });
    }
  
    return authenticate;
  }
docs: Return a function that authenticates the user. The user is identified by email.
  The hashed password is passed to the User model for authentication.
  @param {Model} authModel - The mongoose model used to authenticate the user
  @param {Object} [config] - The application configuration, may be passed to the service some day
  @returns {function} - The authentication function to use with the given authModel