This minimal OAuth provider:

1. Stateless except for temporary KV storage - Only stores the API key for 10 minutes in KV during the auth flow
2. Uses cookie for repeat visits - Saves the API key in a cookie for convenience on repeat visits
3. Simple flow:
   • /authorize shows a clean form asking for API key
   • User enters API key, it gets stored in KV with a temporary auth code
   • /token exchanges the auth code for the API key and deletes it from KV
4. Proper OAuth compliance - Includes all the required metadata endpoints

To use it on any server:

npm i parallel-oauth-provider

import { parallelOauthProvider } from "parallel-oauth-provider";

export default {
  async fetch(request, env) {
    const oauthResponse = await parallelOauthProvider(
      request,
      // Must have {get,put,delete}
      env.KV,
      // Encryption Secret
      env.SECRET,
      // Optional config
      { pathPrefix: "/oauth", assetsPrefix: "/assets/oauth" }
    );
    if (oauthResponse) return oauthResponse;

    // Your other routes...
  },
};

It has been abstracted away fully from Cloudflare and can be used in any cloud provider that allows JavaScript. It uses the KV API equal to that of Cloudflare KV.

See demo in combination with index.html

The user just needs to get their API key from the Parallel dashboard and enter it once - it'll be remembered in a cookie for future use.