[IMP] peek into the JWT to get the channel uuid

ThanhDodeurOdoo · ThanhDodeurOdoo · commit 76fb87f4e770 · 2025-04-23T14:52:19.000+02:00
Before this commit, the payload of the first websocket message (auth)
would expect the channel uuid along the jwt, to know where to look
to get the key used to sign it.

It was slightly redundant as the channel uuid is part of the jwt
payload. With the new JWT implementation, we now have the freedom
to read the JWT before verifying it.

It also reduces the business code complexity as we no longer need to
check the corner case of passing a keyed channel uuid in the jwt
while skipping the channelUUID of the websocket payload (see removed
code in `connect()` of `ws.js`.

This is safe to do as the payload is verified with the key of the
channel, which means that the signature has to match the channel uuid
and tampering with it would invalidate the content.
diff --git a/src/services/auth.js b/src/services/auth.js
@@ -34,6 +34,14 @@ import { AuthenticationError } from "#src/utils/errors.js";
  * @property {string} [jti] - JWT ID
  */
 
+/**
+ * @typedef {Object} JWTData
+ * @property {JWTHeader} header - The JWT header
+ * @property {JWTClaims} claims - The JWT claims
+ * @property {Buffer} signature - The JWT signature
+ * @property {string} signedData - The signed data (header + claims)
+ */
+
 let jwtKey;
 const logger = new Logger("AUTH");
 const ALGORITHM = {
@@ -84,7 +92,7 @@ function base64Decode(str) {
  * Signs and creates a JsonWebToken
  *
  * @param {JWTClaims} claims - The claims to include in the token
- * @param {WithImplicitCoercion<string>} [key] - Optional key, defaults to the configured jwtKey
+ * @param {WithImplicitCoercion<string> | Buffer} [key] - Optional key, defaults to the configured jwtKey
  * @param {Object} [options]
  * @param {string} [options.algorithm] - The algorithm to use, defaults to HS256
  * @returns {string} - The signed JsonWebToken
@@ -144,31 +152,53 @@ function safeEqual(a, b) {
  * @throws {AuthenticationError}
  */
 export function verify(jsonWebToken, key = jwtKey) {
-    const keyBuffer = Buffer.isBuffer(key) ? key : Buffer.from(key, "base64");
-    let parsedJWT;
-    try {
-        parsedJWT = parseJwt(jsonWebToken);
-    } catch {
-        throw new AuthenticationError("Invalid JWT format");
-    }
-    const { header, claims, signature, signedData } = parsedJWT;
-    const expectedSignature = ALGORITHM_FUNCTIONS[header.alg]?.(signedData, keyBuffer);
-    if (!expectedSignature) {
-        throw new AuthenticationError(`Unsupported algorithm: ${header.alg}`);
-    }
-    if (!safeEqual(signature, expectedSignature)) {
-        throw new AuthenticationError("Invalid signature");
-    }
-    // `exp`, `iat` and `nbf` are in seconds (`NumericDate` per RFC7519)
-    const now = Math.floor(Date.now() / 1000);
-    if (claims.exp && claims.exp < now) {
-        throw new AuthenticationError("Token expired");
-    }
-    if (claims.nbf && claims.nbf > now) {
-        throw new AuthenticationError("Token not valid yet");
+    const jwt = new JsonWebToken(jsonWebToken);
+    return jwt.verify(key);
+}
+
+export class JsonWebToken {
+    /**
+     * @type {JWTData}
+     */
+    unsafe;
+    /**
+     * @param {string} jsonWebToken
+     */
+    constructor(jsonWebToken) {
+        let payload;
+        try {
+            payload = parseJwt(jsonWebToken);
+        } catch {
+            throw new AuthenticationError("Malformed JWT");
+        }
+        this.unsafe = payload;
     }
-    if (claims.iat && claims.iat > now + 60) {
-        throw new AuthenticationError("Token issued in the future");
+
+    /**
+     * @param {WithImplicitCoercion<string>} [key] buffer/b64 str
+     * @return {JWTClaims}
+     */
+    verify(key = jwtKey) {
+        const { header, claims, signature, signedData } = this.unsafe;
+        const keyBuffer = Buffer.isBuffer(key) ? key : Buffer.from(key, "base64");
+        const expectedSignature = ALGORITHM_FUNCTIONS[header.alg]?.(signedData, keyBuffer);
+        if (!expectedSignature) {
+            throw new AuthenticationError(`Unsupported algorithm: ${header.alg}`);
+        }
+        if (!safeEqual(signature, expectedSignature)) {
+            throw new AuthenticationError("Invalid signature");
+        }
+        // `exp`, `iat` and `nbf` are in seconds (`NumericDate` per RFC7519)
+        const now = Math.floor(Date.now() / 1000);
+        if (claims.exp && claims.exp < now) {
+            throw new AuthenticationError("Token expired");
+        }
+        if (claims.nbf && claims.nbf > now) {
+            throw new AuthenticationError("Token not valid yet");
+        }
+        if (claims.iat && claims.iat > now + 60) {
+            throw new AuthenticationError("Token issued in the future");
+        }
+        return claims;
     }
-    return claims;
 }
diff --git a/src/services/ws.js b/src/services/ws.js
@@ -7,11 +7,11 @@ import { Logger, extractRequestInfo } from "#src/utils/utils.js";
 import { AuthenticationError, OvercrowdedError } from "#src/utils/errors.js";
 import { SESSION_CLOSE_CODE } from "#src/models/session.js";
 import { Channel } from "#src/models/channel.js";
-import { verify } from "#src/services/auth.js";
+import { JsonWebToken } from "#src/services/auth.js";
 
 /**
  * @typedef Credentials
- * @property {string} channelUUID
+ * @property {string} channelUUID deprecated, this is obtained from the jwt
  * @property {string} jwt
  */
 
@@ -53,7 +53,6 @@ export async function start(options) {
                 /** @type {Credentials | String} can be a string (the jwt) for backwards compatibility with version 1.1 and earlier */
                 const credentials = JSON.parse(message);
                 const session = connect(webSocket, {
-                    channelUUID: credentials?.channelUUID,
                     jwt: credentials.jwt || credentials,
                 });
                 session.remote = remoteAddress;
@@ -102,22 +101,14 @@ export function close() {
  * @param {import("ws").WebSocket} webSocket
  * @param {Credentials}
  */
-function connect(webSocket, { channelUUID, jwt }) {
-    let channel = Channel.records.get(channelUUID);
-    const authResult = verify(jwt, channel?.key);
-    const { sfu_channel_uuid, session_id, ice_servers } = authResult;
-    if (!channelUUID && sfu_channel_uuid) {
-        // Cases where the channelUUID is not provided in the credentials for backwards compatibility with version 1.1 and earlier.
-        channel = Channel.records.get(sfu_channel_uuid);
-        if (channel.key) {
-            throw new AuthenticationError(
-                "A channel with a key can only be accessed by providing a channelUUID in the credentials"
-            );
-        }
-    }
+function connect(webSocket, { jwt }) {
+    const token = new JsonWebToken(jwt);
+    const channel = Channel.records.get(token.unsafe.claims.sfu_channel_uuid);
     if (!channel) {
         throw new AuthenticationError(`Channel does not exist`);
     }
+    const authResult = token.verify(channel.key);
+    const { session_id, ice_servers } = authResult;
     if (!session_id) {
         throw new AuthenticationError("Malformed JWT payload");
     }
diff --git a/tests/network.test.js b/tests/network.test.js
@@ -264,7 +264,7 @@ describe("Full network", () => {
         expect(closeEvent.code).toBe(SESSION_CLOSE_CODE.P_TIMEOUT);
     });
     test("A client can broadcast arbitrary messages to other clients on a channel that does not have webRTC", async () => {
-        const channelUUID = await network.getChannelUUID(false);
+        const channelUUID = await network.getChannelUUID({ useWebRtc: false });
         const user1 = await network.connect(channelUUID, 1);
         const user2 = await network.connect(channelUUID, 2);
         const sender = await network.connect(channelUUID, 3);
diff --git a/tests/security.test.js b/tests/security.test.js
@@ -39,4 +39,17 @@ describe("Security", () => {
         const [event] = await once(websocket, "close");
         expect(event).toBe(WS_CLOSE_CODE.TIMEOUT);
     });
+    test("cannot use the default jwt to sign a keyed channel", async () => {
+        const channelUUID = await network.getChannelUUID({ key: "channel-specific-key" });
+        const channel = Channel.records.get(channelUUID);
+        await expect(network.connect(channelUUID, 3)).rejects.toThrow();
+        expect(channel.sessions.size).toBe(0);
+    });
+    test("can create and join a keyed channel with the appropriate key", async () => {
+        const key = "channel-specific-key";
+        const channelUUID = await network.getChannelUUID({ key });
+        const channel = Channel.records.get(channelUUID);
+        await network.connect(channelUUID, 4, { key });
+        expect(channel.sessions.size).toBe(1);
+    });
 });
diff --git a/tests/utils/network.js b/tests/utils/network.js
@@ -12,8 +12,8 @@ import { Channel } from "#src/models/channel.js";
 const HMAC_B64_KEY = "u6bsUQEWrHdKIuYplirRnbBmLbrKV5PxKG7DtA71mng=";
 const HMAC_KEY = Buffer.from(HMAC_B64_KEY, "base64");
 
-export function makeJwt(data) {
-    return auth.sign(data, HMAC_KEY, { algorithm: "HS256" });
+export function makeJwt(data, { key = HMAC_KEY } = {}) {
+    return auth.sign(data, key, { algorithm: "HS256" });
 }
 
 /**
@@ -44,13 +44,15 @@ export class LocalNetwork {
     }
 
     /**
-     * @param {boolean} [useWebRtc]
+     * @param {Object} [param0]
+     * @param {boolean} [useWebRtc=true]
+     * @param {string} [key] the channel-specific key
      * @returns {Promise<string>}
      */
-    async getChannelUUID(useWebRtc = true) {
+    async getChannelUUID({ useWebRtc = true, key = HMAC_B64_KEY } = {}) {
         const jwt = this.makeJwt({
             iss: `http://${this.hostname}:${this.port}/`,
-            key: HMAC_B64_KEY,
+            key,
         });
         const response = await fetch(
             `http://${this.hostname}:${this.port}/v${http.API_VERSION}/channel?webRTC=${useWebRtc}`,
@@ -70,10 +72,12 @@ export class LocalNetwork {
      *
      * @param {string} channelUUID
      * @param {number} sessionId
+     * @param {Object} [options]
+     * @param {string} [options.key] the key to use to authenticate the session (this should be the key of the channel)
      * @returns { Promise<{ session: import("#src/models/session.js").Session, sfuClient: import("#src/client.js").SfuClient }>}
      * @throws {Error} if the client is closed before being authenticated
      */
-    async connect(channelUUID, sessionId) {
+    async connect(channelUUID, sessionId, { key = HMAC_KEY } = {}) {
         const sfuClient = new SfuClient();
         this._sfuClients.push(sfuClient);
         sfuClient._createDevice = () => {
@@ -100,10 +104,13 @@ export class LocalNetwork {
         });
         sfuClient.connect(
             `ws://${this.hostname}:${this.port}`,
-            this.makeJwt({
-                sfu_channel_uuid: channelUUID,
-                session_id: sessionId,
-            }),
+            this.makeJwt(
+                {
+                    sfu_channel_uuid: channelUUID,
+                    session_id: sessionId,
+                },
+                { key }
+            ),
             { channelUUID }
         );
         const channel = Channel.records.get(channelUUID);
