I have the following code that does not execute (I get back 500 internal server error).

What did I do wrong?

app.post('/api/sign-in', function (req, res, next) {
    //auth
    firebase.auth().signInWithEmailAndPassword(req.query.username, req.query.password)
        //get back promise, log user object's email address
        .then(function (user) {
            console.log(user.email)
        })
        //log error
        .catch(function (error) {
            console.log(error);
        })
});