/openrouter-oauth

name: openrouter-oauth
description: Implement "Sign In with OpenRouter" using OAuth PKCE — framework-agnostic, no SDK or client registration required. Use when the user wants to add OpenRouter login, authentication, sign-in buttons, OAuth, or AI model inference API keys for browser-based apps. No client registration, no backend, no secrets required.
version: 2.0.0
compatibility: browser (requires Web Crypto API, localStorage, sessionStorage)

Sign In with OpenRouter

Add OAuth login to any web app. Users authorize on OpenRouter and your app receives an API key — no client registration, no backend, no secrets. Works with any framework.

Live demo: [openrouterteam.github.io/sign-in-with-openrouter](https://openrouterteam.github.io/sign-in-with-openrouter/)

Decision Tree

| User wants to… | Do this | |---|---| | Add sign-in / login to a web app | Follow the full PKCE flow + button guidance below | | Get an API key programmatically (no UI) | Just implement the PKCE flow — skip the button section | | Use the OpenRouter SDK after auth | Do PKCE here for the key, then see `openrouter-typescript-sdk` skill for `callModel`/streaming |

---

OAuth PKCE Flow

No client ID or secret — the PKCE challenge is the only proof of identity.

Step 1: Generate verifier and challenge

code_verifier  = base64url(32 random bytes)
code_challenge = base64url(SHA-256(code_verifier))

• Use `crypto.getRandomValues(new Uint8Array(32))` for the random bytes
• base64url encoding: standard base64, then replace `+` → `-`, `/` → `_`, strip trailing `=`
• Store `code_verifier` in **`sessionStorage`** (not `localStorage`) — so the verifier doesn't persist after the tab closes or leak to other tabs (security: the verifier is a one-time secret)

Step 2: Redirect to OpenRouter

https://openrouter.ai/auth?callback_url={url}&code_challenge={challenge}&code_challenge_method=S256

| Param | Value | |---|---| | `callback_url` | Your app's URL (where the user returns after auth) | | `code_challenge` | The S256 challenge from Step 1 | | `code_challenge_method` | Always `S256` |

Step 3: Handle the redirect back

User returns to your `callback_url` with `?code=` appended. Extract the `code` query parameter.

**Important:** Before processing `?code=`, check that a `code_verifier` exists in `sessionStorage`. Other routes or third-party code might use `?code=` query params for unrelated purposes — a `hasOAuthCallbackPending()` guard ensures you only consume codes that belong to your OAuth flow.

Step 4: Exchange code for API key

POST https://openrouter.ai/api/v1/auth/keys
Content-Type: application/json

{
  "code": "<code from query param>",
  "code_verifier": "<verifier from sessionStorage>",
  "code_challenge_method": "S256"
}

→ { "key": "sk-or-..." }

Remove the verifier from `sessionStorage` before or after the exchange.

Step 5: Store the key and clean up

• Store `key` in `localStorage`
• Clean the URL: `history.replaceState({}, "", location.pathname)` to remove `?code=`
• **Cross-tab sync:** Listen for `storage` events on the API key's `localStorage` entry so other tabs update when the user signs in or out

---

Auth Module Reference

Drop-in module implementing the full PKCE flow. Reduces risk of getting base64url encoding, sessionStorage handling, or the key exchange wrong.

// lib/openrouter-auth.ts
const STORAGE_KEY = "openrouter_api_key";
const VERIFIER_KEY = "openrouter_code_verifier";

type AuthListener = () => void;
const listeners = new Set<AuthListener>();
export const onAuthChange = (fn: AuthListener) => { listeners.add(fn); return () => listeners.delete(fn); };
const notify = () => listeners.forEach((fn) => fn());

// Cross-tab sync: other tabs update when user signs in/out
if (typeof window !== "undefined") {
  window.addEventListener("storage", (e) => { if (e.key === STORAGE_KEY) notify(); });
}

export const getApiKey = (): string | null =>
  typeof window !== "undefined" ? localStorage.getItem(STORAGE_KEY) : null;

export const setApiKey = (key: string) => { localStorage.setItem(STORAGE_KEY, key); notify(); };
export const clearApiKey = () => { localStorage.removeItem(STORAGE_KEY); notify(); };

// Guard: only process ?code= if we initiated an OAuth flow in this tab
export const hasOAuthCallbackPending = (): boolean =>
  typeof window !== "undefined" && sessionStorage.getItem(VERIFIER_KEY) !== null;

function generateCodeVerifier(): string {
  const bytes = new Uint8Array(32);
  crypto.getRandomValues(bytes);
  return btoa(String.fromCharCode(...bytes))
    .replace(/\+/g, "-").replace(/\//g, "_").replace(/=+$/, "");
}

async function computeS256Challenge(verifier: string): Promise<string> {
  const digest = await crypto.subtle.digest("SHA-256", new TextEncoder().encode(verifier));
  return btoa(String.fromCharCode(...new Uint8Array(digest)))
    .replace(/\+/g, "-").replace(/\//g, "_").replace(/=+$/, "");
}

export async function initiateOAuth(callbackUrl?: string): Promise<void> {
  const verifier = generateCodeVerifier();
  sessionStorage.setItem(VERIFIER_KEY, verifier);
  const challenge = await computeS256Challenge(verifier);
  const url = callbackUrl ?? window.location.origin + window.location.pathname;
  window.location.href = `https://openrouter.ai/auth?${new URLSearchParams({
    callback_url: url, code_challenge: challenge, code_challenge_method: "S256",
  })}`;
}

export async function handleOAuthCallback(code: string): Promise<void> {
  const verifier = sessionStorage.getItem(VERIFIER_KEY);
  if (!verifier) throw new Error("Missing code verifier");
  sessionStorage.removeItem(VERIFIER_KEY);
  const res = await fetch("https://openrouter.ai/api/v1/auth/keys", {
    method: "POST",
    headers: { "Content-Type": "application/json" },
    body: JSON.stringify({ code, code_verifier: verifier, code_challenge_method: "S256" }),
  });
  if (!res.ok) throw new Error(`Key exchange failed (${res.status})`);
  const { key } = await res