Update readme - add new options and BFF example

readme.md

@@ -8,6 +8,10 @@ The authentication library allows you to easily authenticate with the Elfsquad A
 - `redirectUri` callback entry point of your app.
 - `scope` (optional) Requested authentication scope. Defaults to `Elfskot.Api offline_access`.
 - `loginUrl` (optional) URL of the authentication service. Defaults to `https://login.elfsquad.io`.
+- `responseMode` (optional) OAuth response mode, either `'fragment'` or `'query'`. Defaults to `'fragment'`.
+- `storeRefreshToken` (optional) Callback to store the refresh token server-side. When provided, the library will call this instead of saving the token to `localStorage`. Must be provided together with `refreshAccessToken` and `revokeRefreshToken`.
+- `refreshAccessToken` (optional) Callback to refresh the access token via a server-side endpoint. When provided, the library will call this instead of using the built-in `localStorage`-based refresh flow. Must be provided together with `storeRefreshToken` and `revokeRefreshToken`.
+- `revokeRefreshToken` (optional) Callback to revoke the server-side refresh token on sign-out. Must be provided together with `storeRefreshToken` and `refreshAccessToken`.
 
 ## Methods
 
@@ -43,3 +47,31 @@ authenticationContext.isSignedIn().then((isSignedIn) => {
   }
 });
 ```
+
+### BFF pattern (secure refresh token storage)
+
+Use the `storeRefreshToken`, `refreshAccessToken`, and `revokeRefreshToken` callbacks to move refresh tokens out of `localStorage` into server-side HttpOnly cookies, eliminating XSS exposure of long-lived credentials.
+
+```js
+import { AuthenticationContext } from "@elfsquad/authentication";
+
+const authenticationContext = new AuthenticationContext({
+  clientId: "c2a349a9-02ea-4e1e-a59d-65870529f713",
+  redirectUri: "https://example.com",
+  storeRefreshToken: (token) =>
+    fetch("/auth/store-token", {
+      method: "POST",
+      body: JSON.stringify({ token }),
+    }).then(() => {}),
+  refreshAccessToken: () =>
+    fetch("/auth/refresh").then((r) => r.json()),
+  revokeRefreshToken: () =>
+    fetch("/auth/revoke", { method: "POST" }).then(() => {}),
+});
+
+authenticationContext.onSignIn().then(() => {
+  authenticationContext.getAccessToken().then((accessToken) => {
+    console.log("accessToken", accessToken);
+  });
+});
+```