token changed callback

README.md

@@ -256,6 +256,28 @@ const client = new Client(authClient);
 const result = await client.createInvoice({amount: 1000});
 ```
 
+#### Handling refresh token 
+Access tokens do expire. If an access token is about to expire, this library will automatically use a refresh token to retrieve a fresh one. Utilising the tokens event is a simple approach to guarantee that you always save the most recent tokens:
+
+```js
+const token = loadTokenForUser(); // {access_token: string, refresh_token: string, expires_at: number}
+const authClient = new auth.OAuth2User({
+  client_id: process.env.CLIENT_ID,
+  callback: "http://localhost:8080/callback",
+  scopes: ["invoices:read", "account:read", "balance:read", "invoices:create", "invoices:read", "payments:send"],
+  token: token
+});
+
+// listen to the tokens event
+authClient.on('tokens', (tokens) => {
+  if (tokens.refresh_token) {
+    // store the tokens in database
+    console.log(tokens.refresh_token);
+  }
+  console.log(tokens.access_token);
+});
+```
+
 #### Sending payments
 
 ```js

package.json

@@ -32,7 +32,8 @@
   },
   "dependencies": {
     "crypto-js": "^4.1.1",
-    "nostr-tools": "1.13.1"
+    "nostr-tools": "1.13.1",
+    "events": "^3.3.0"
   },
   "devDependencies": {
     "@types/crypto-js": "^4.1.1",

src/OAuth2User.ts

@@ -2,6 +2,7 @@ import CryptoJS from 'crypto-js';
 import { buildQueryString, basicAuthHeader } from "./utils";
 import { OAuthClient, AuthHeader, GetTokenResponse, Token, GenerateAuthUrlOptions } from "./types";
 import { RequestOptions, rest } from "./request";
+import EventEmitter from 'events';
 
 const AUTHORIZE_URL = "https://getalby.com/oauth";
 
@@ -23,6 +24,8 @@ export interface OAuth2UserOptions {
   token?: Token;
 }
 
+export type EventName= "tokens";
+
 function processTokenResponse(token: GetTokenResponse): Token {
   const { expires_in, ...rest } = token;
   return {
@@ -39,13 +42,21 @@ export class OAuth2User implements OAuthClient {
   code_verifier?: string;
   code_challenge?: string;
   private _refreshAccessTokenPromise: Promise<{token: Token}> | null;
+  private _tokenEvents = new EventEmitter();
   constructor(options: OAuth2UserOptions) {
     const { token, ...defaultOptions } = options;
     this.options = {client_secret: '', ...defaultOptions};
     this.token = token;
     this._refreshAccessTokenPromise = null;
   }
 
+    /**
+   * Subscribe to the events
+   */
+  async on(eventName: EventName, listener: (tokens: Token) => void): Promise<void> {
+    this._tokenEvents.on(eventName, listener);
+  }
+
   /**
    * Refresh the access token
    */
@@ -177,7 +188,10 @@ export class OAuth2User implements OAuthClient {
 
   async getAuthHeader(): Promise<AuthHeader> {
     if (!this.token?.access_token) throw new Error("access_token is required");
-    if (this.isAccessTokenExpired()) await this.refreshAccessToken();
+    if (this.isAccessTokenExpired()){ 
+      await this.refreshAccessToken()
+      this._tokenEvents.emit("tokens", this.token);
+    };
     return {
       Authorization: `Bearer ${this.token.access_token}`,
     };

yarn.lock

@@ -3090,7 +3090,7 @@ eventemitter3@^4.0.4:
   resolved "https://registry.yarnpkg.com/eventemitter3/-/eventemitter3-4.0.7.tgz#2de9b68f6528d5644ef5c59526a1b4a07306169f"
   integrity sha512-8guHBZCwKnFhYdHr2ysuRWErTwhoN2X8XELRlrRwpmfeY2jjuUN4taQMsULKUVo1K4DvZl+0pgfyoysHxvmvEw==
 
-events@^3.0.0:
+events@^3.0.0, events@^3.3.0:
   version "3.3.0"
   resolved "https://registry.yarnpkg.com/events/-/events-3.3.0.tgz#31a95ad0a924e2d2c419a813aeb2c4e878ea7400"
   integrity sha512-mQw+2fkQbALzQ7V0MY0IqdnXNOeTtP4r0lN9z7AAawCXgqea7bDii20AYrIBrFd/Hx0M2Ocz6S111CaFkUcb0Q==