Have you ever wondered how challenging it is to create a Custom GPT with user authentication and database access? I found the lack of examples of this disheartening. So, I create a comprehensive guide myself and am pleased to say, with a small amount of coding skills you can build your own in day.

Tech Stack

To achieve this, I used:

Clerk.com: for authentication
Vercel: for hosting
Prisma: for great database management UX
Neon: for serverless postgres
Typescript
Express.js

Who is this for?

This guide is perfect for developers looking to create an AI Agent or a Custom GPT that supports user authentication and database access with ease.

Why it matters

An AI Agent with user authentication unlocks numerous possibilities, enabling applications that require secure user data access and personalized experiences.

Prerequisites

Before diving in you will need:

Familiarity with DNS and configuring a Custom Domain Name
Familiarity with creating a REST API
Have a paid subscription to ChatGPT

Background Story

In my quest to build GPTs with authentication, I found the lack of examples disheartening. Despite extensive searches on Perplexity, Arc Search, and ChatGPT, the closest resources were:

Authenticate users in GPT actions: Build a personal agenda assistant - Too closely tied to Logto.io
How to add OAuth authorization for custom GPTs - Using PHP, Laravel, and looks overly complicated
GPT Action with Google OAuth) - Limited to Google APIs
GPT-Actions: GPT Auth - Not using OAuth2

Since I couldn’t find what I needed, I decided to create an example myself, hoping it would help others in similar situations.

The Challenge

After getting the basics working and configuring the GPT, I faced a frustratingly generic error when trying to save:

To troubleshoot, I built another Custom GPT using OAuth2 to access my Google Calendar, confirming the issue was specific to my project. The community shared similar frustrations:
"Error saving draft" when creating an authenticated action in a GPT

The Solution

The breakthrough came from an unusual requirement in the OpenAI docs: the OAuth2 server must share the same domain as the API server, except for Google, Microsoft, and Adobe OAuth domains.

Once I configured a custom domain on Clerk, everything worked beautifully! The result is a template project that any developer with at least two years of experience can fork, customize, and deploy in a single day.
* GitHub Repository: Custom GPT API OAuth

Demo

Check out the demo for a hands-on experience. Feel free to explore, and even spam the database - restoring it is easy with backups on Neon.

Demo: My Pizza Dough - OAuth Demo

Checkout the rest of my series on GPTs: ~Who Cares About Custom GPTs?~

Build a GPT That Talks to Your Database in One Day