FRONT END

signIn(){
	  	var signInData = {
	  		username : ReactDOM.findDOMNode(this.refs.logInUser).value,
	  		password : ReactDOM.findDOMNode(this.refs.logInPass).value
	  		};

		$.ajax({
			  type: "POST",
			  url: "/loginAuth",
			  data: signInData,
			  dataType: "json",
			  success: function(){
				window.location.href= "./";
			  },
			  error: function(){
			    alert("Either your email or password is wrong!");
			  }
		});
}

AUTH.JS


app.post('/loginAuth', function(req, res, next) {
  passport.authenticate('local', function(err, user, info) {
    if (err) {
      return next(err);
    }
    if (!user) {
      return res.status(401);
    }
    req.logIn(user, function(err) {
      if (err) {
        return next(err);
      }
      return res.status(200);
    });
  })(req, res, next);
});



passport.use(new LocalStrategy({
  usernameField: 'username',
  passwordField: 'password',
  passReqToCallback: true
},

  function(req, username, password, done) { // callback with email and password from our form

    connection.query("SELECT * FROM `users` WHERE `username` = '" + username + "'",function(err,rows){
      if (err)
        return done(err);
      if (!rows.length) {
        return done(null, false);
      }
        // if the user is found but the password is wrong
      if (!( rows[0].password == password)) {
        return done(null, false); // create the loginMessage and save it to session as flashdata
      } else {
              // all is well, return successful user
        return done(null, rows[0].username);
      }

    });
}));