<form is="iron-form" id="form" >
      <paper-input name="userEmail" label="Email" required></paper-input>
      <paper-input name="password" type="password" label="Password" required></paper-input>
      <br>
      <paper-button raised
          on-click="login">Submit</paper-button>
    </form>

<script>
  (function() {
    Polymer({
        is: 'module-login',
        login: function() {
            // this is used to trigger Polymer's form validation
            Polymer.dom(event).localTarget.parentElement.submit();

            // this is my ajax request
            this.$.auth.login(this.$.userEmail.value, this.$.password.value);
        }
    });
 })();
</script>