signIn.js

Parse.Cloud.define('signIn', function (req, res) {

    var email = req.params.email.toLowerCase();

    Parse.User.logIn(email, req.params.password).then(function (user) {
        res.success(user);
    }, function (error) {
        if (error.code === Parse.Error.INVALID_SESSION_TOKEN) {
            Parse.User.logOut();
        }
        console.log("Error: " + error.code + " " + error.message);
        res.error(error.message);
    });
});