<iron-ajax id="ajaxUser"
  url="http://localhost:8080/login"
  method="post"
  handle-as="json"
  params="[[params]]"
  on-response="saveUserCredentials"
  last-response="{{user}}"></iron-ajax>

<paper-input id="username"></paper-input>
<paper-input id="password"></paper-input>
<paper-button on-tap="loginUser"></paper-button>

loginUser() {
  this.params = {"username": this.$.username.value, "password": this.$.password.value};
  console.log(this.params); // logs this.params as populated JSON
  let request = this.$.ajaxUser.generateRequest();
  request.completes.then(req => {
    console.log(req);       // logs <iron-request></iron-request>
    console.log(this.user); // logs []
  })
  .catch(rejected => {
    console.log(rejected.request); // not returned
    console.log(rejected.error);   // not returned
  })
}

saveUserCredentials() {
  console.log(this.user);
}

app.post("/login", (req, res) => {
  session.login(req, res)
})

exports.login = (req, res) => {
  sql.connect(config.properties)
    .then(pool => {
      pool.request()
        .input('user', sql.VarChar(50), req.body.username)
        .input('password', sql.VarChar(50), req.body.password)
        .query("SELECT role FROM Login WHERE username = @user AND password = @password")
        .then(response => res.send(response))
        .catch(err => res.send(err))
    })
}