StartGG OAuth2 + PKCE Toolkit (TypeScript)

Drop-in utilities for OAuth 2.0 Authorization Code with PKCE and Bearer usage against Start.gg (or any RFC-compliant OAuth2 provider).

• ✅ RFCs: 6749 (OAuth2), 6750 (Bearer), 7636 (PKCE)
• ✅ PKCE S256, high-entropy verifier
• ✅ application/x-www-form-urlencoded token requests
• ✅ Scope-safe validation (assume unchanged when scope omitted)
• ✅ Robust error surfaces (JSON/text)
• ✅ Skew-aware expiry helper (BearerToken)
• ✅ Cross-env: Browser + Node (WebCrypto + fetch)
• ✅ CI: Jest + TypeScript build on push/PR

Cooked for you by 0xabadbabe - using a lot of 💜 and few lines of code. ... with hope tha this would help for any dev struggling with oauth2 start.gg specific.

┬─[playerone@fedora:~/d/startgg-oauth2-full]─[21:08:50]─[G:main =]
╰─>$ npm test -- pkce

> [email protected] test
> jest --runInBand pkce

 PASS  __tests__/pkce.test.ts
  PKCE helpers
    ✓ generateCodeVerifier length bounds (4 ms)
    ✓ computeCodeChallengeS256 deterministic (3 ms)

Test Suites: 1 passed, 1 total
Tests:       2 passed, 2 total
Snapshots:   0 total
Time:        0.641 s, estimated 1 s
Ran all test suites matching /pkce/i.
┬─[playerone@fedora:~/d/startgg-oauth2-full]─[21:10:09]─[G:main =]
╰─>$ 
[0] 0:fish*                                                                  "~/d/startgg-oauth2-fu" 21:10 30-lis-25

Installation

npm i startgg-oauth2-full
# or copy src/auth/StartGGOAuth2.ts into your project

GitHub Packages (optional)

This library is also mirrored to GitHub Packages if your environment prefers that registry:

npm set //npm.pkg.github.com/:_authToken=<GH_TOKEN_WITH_PACKAGES_SCOPE>
npm install @0xabadbabe-ops/startgg-oauth2-full

Requirements

• Browser: window.crypto.subtle, window.crypto.getRandomValues, fetch
• Node: 18+ (built-in WebCrypto + fetch)

Quick Start

Browser (PKCE → Exchange)

import { buildAuthorizeUrl, StartGGScope } from 'startgg-oauth2-full';

const cfg = {
  clientId: '<client-id>',
  authEndpoint: 'https://api.start.gg/oauth/authorize',
  redirectUri: 'https://your.app/api/startgg/callback',
};

const { url, codeVerifier } = await buildAuthorizeUrl(cfg, {
  scopes: [StartGGScope.USER_IDENTITY, StartGGScope.USER_EMAIL],
  state: crypto.randomUUID(),
});

sessionStorage.setItem('pkce:verifier', codeVerifier);
sessionStorage.setItem('oauth:state', '<same-state>');
location.href = url;

Callback (Exchange + Bearer)

import { createStartGGAuth2Handler, BearerToken, StartGGScope } from 'startgg-oauth2-full';

const params = new URLSearchParams(location.search);
const code = params.get('code')!;
const state = params.get('state')!;
if (state !== sessionStorage.getItem('oauth:state')) throw new Error('State mismatch');

const handler = createStartGGAuth2Handler({
  clientId: '<client-id>',
  redirectUri: 'https://your.app/api/startgg/callback',
  authEndpoint: 'https://api.start.gg/oauth/authorize',
  tokenEndpoint: 'https://api.start.gg/oauth/token',
});

const res = await handler.exchangeToken(code, sessionStorage.getItem('pkce:verifier')!, [
  StartGGScope.USER_IDENTITY,
  StartGGScope.USER_EMAIL,
]);

const bearer = BearerToken.fromOAuthResponse(res);
fetch('https://api.start.gg/your-endpoint', { headers: bearer.toAuthHeader() });

Scripts

npm run build      # tsc build
npm test           # Jest tests (needs ts-node installed)

Examples ship as their own workspaces—hop into each folder, install once, then use the local scripts:

• Browser (Vite): cd examples/browser && npm install && npm run dev
• Node CLI/server: cd examples/node && npm install && npm run dev
• Discord.js bot: cd examples/discordjs && npm install && npm run dev
• Next.js app: cd examples/nextjs && npm install && npm run dev
• Frontend Vite demo: cd examples/vite && npm install && npm run dev

API (summary)

• generateCodeVerifier(len?: number): string
• computeCodeChallengeS256(verifier: string): Promise<string>
• buildAuthorizeUrl(cfg, opts): Promise<{ url, codeVerifier, codeChallenge }>
• createStartGGAuth2Handler(cfg): StartGGOAuth2Handler
  • exchangeToken(code, codeVerifier, expectedScopes)
  • refreshToken(refreshToken, originalScopes)
• BearerToken
  • fromOAuthResponse(res, nowMs?, skewSeconds?)
  • isExpired(), willExpireWithin(), toAuthHeader(), assertUsable()

Scopes

enum StartGGScope {
  USER_IDENTITY = 'user.identity',
  USER_EMAIL = 'user.email',
  TOURNAMENT_MANAGER = 'tournament.manager',
  TOURNAMENT_REPORTER = 'tournament.reporter',
}

Scope Semantics

• If response includes scope, it’s validated; missing required → ScopeValidationError.
• If response omits scope, treat as unchanged (RFC 6749).
• Refresh: preserve prior refresh_token if omitted by server.

Error Model

class OAuth2Error extends Error {
  code?: string;     // e.g., TOKEN_EXCHANGE_FAILED
  details?: unknown; // parsed JSON or { raw: string }
}

Examples

• Browser (Vite SPA): examples/browser/
• Node CLI + redirect catcher: examples/node/
• Discord bot (discord.js v14): examples/discordjs/
• Next.js (App Router): examples/nextjs/
• Frontend Vite scaffold: examples/vite/

CI

GitHub Actions runs TypeScript build + Jest on push/PR (Node 18 & 20). See .github/workflows/ci.yml.

Repository Tree

startgg-oauth2-full/
├── README.md
├── AGENTS.md
├── LICENSE
├── package.json
├── tsconfig.json
├── jest.config.ts
├── jest.setup.ts
├── .gitignore
├── .npmrc
├── src/
│   └── auth/
│       └── StartGGOAuth2.ts
├── __tests__/
│   ├── authorize-url.test.ts
│   ├── bearer-token.test.ts
│   ├── handler.test.ts
│   └── pkce.test.ts
├── examples/
│   ├── browser/      # Vanilla browser Vite demo
│   ├── node/         # CLI + local redirect server
│   ├── discordjs/    # Discord bot OAuth flow
│   ├── nextjs/       # Next.js App Router example
│   └── vite/         # Minimal Vite SPA scaffold
└── .github/
    ├── ISSUE_TEMPLATE/
    │   ├── bug_report.md
    │   └── feature_request.md
    └── workflows/
        └── ci.yml

Security Notes

• Use and verify state.
• Keep code_verifier private.
• Never log tokens; always HTTPS.

License

MIT License Copyright © 2026 0xABADBABE-ops

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.