added README

Author: Code-Hex

README.md

@@ -0,0 +1,45 @@
+# firebase-auth-cloudflare-workers
+
+**Zero-dependencies** firebase auth verification library for Cloudflare Workers.
+
+- Implemented by only Web Standard API.
+- Supported Firebase Auth Emulator.
+
+```ts
+export async function fetch(req: Request, env: Bindings) {
+  const authorization = req.headers.get('Authorization')
+  if (authorization === null) {
+    return new Response(null, {
+      status: 400,
+    })
+  }
+  const jwt = authorization.replace(/Bearer\s+/i, "")
+  const auth = Auth.getOrInitialize(
+    env.PROJECT_ID,
+    env.PUBLIC_JWK_CACHE_KEY,
+    env.PUBLIC_JWK_CACHE_KV
+  )
+  const firebaseToken = await auth.verifyIdToken(jwt, env)
+
+  return new Response(JSON.stringify(firebaseToken), {
+    headers: {
+      "Content-Type": "application/json"
+    }
+  })
+}
+
+export default { fetch };
+```
+
+## Running example code
+
+I put an [example](https://github.com/Code-Hex/firebase-auth-cloudflare-workers/tree/master/example) directory as Module Worker Syntax. this is explanation how to run the code.
+
+1. Clone this repository and change your directory to it.
+2. Install dev dependencies as `yarn` command.
+3. Run firebase auth emulator by `$ yarn start-firebase-emulator`
+4. Access to Emulator UI in your favorite browser.
+5. Create a new user on Emulator UI. (email: `[email protected]` password: `test1234`)
+6. Run example code on local (may serve as `localhost:8787`) by `$ yarn start-example`
+7. Get jwt for created user by `$ curl -s http://localhost:8787/get-jwt | jq .idToken -r`
+8. Try authorization with user jwt `$ curl http://localhost:8787/ -H 'Authorization: Bearer PASTE-JWT-HERE'`