I have a web app that needs to allow for users to book an appointment. The app loads my calander and shows a visual representation of what timeslots are available from my calander. Each timeslot available was made into a button. When the user clicks the button, it needs to set the event for that time slot. The event details are pre-made, the client doesn't do anything but click the time they want.

Ill be adding a form to accept their email and add it to the "attendees" object so that it can update their calendar.

Using the javascript quickstart, you use

gapi.load('client:auth2', () => {
     gapi.client.init({
       apiKey: API_KEY,
       clientId: CLIENT_ID,
       discoveryDocs: DISCOVERY_DOCS,
       scope: SCOPES,
     });

To get access to my calendar. But the rest of the quickstart

.then(() => {
        gapi.auth2.getAuthInstance().isSignedIn.listen(updateSigninStatus);
      });
function updateSigninStatus() {
        gapi.auth2.getAuthInstance().isSignedIn.get();
      }

Asks the user to sign into their own account using Oauth to add an event...

How do I just allow for them to add an event by clicking the timeslot button, without needing them to go through Oauth?

For visual representation of what it looks like: