Use JWKS to validate incoming JWT auth tokens

package.json

@@ -33,6 +33,7 @@
     "csv-stringify": "^6.5.2",
     "dotenv": "^16.5.0",
     "jsonwebtoken": "^9.0.2",
+    "jwks-rsa": "^3.2.0",
     "lodash": "^4.17.21",
     "reflect-metadata": "^0.2.2",
     "rxjs": "^7.8.1",

src/config/config.env.ts

@@ -31,9 +31,6 @@ export class ConfigEnv {
   @IsString()
   AUTH0_M2M_GRANT_TYPE!: string;
 
-  @IsString()
-  AUTH0_CERT!: string;
-
   @IsString()
   AUTH0_CLIENT_ID!: string;
 

src/core/auth/jwt.ts

@@ -0,0 +1,52 @@
+import { Logger } from '@nestjs/common';
+import { decode } from 'jsonwebtoken';
+import { JwksClient } from 'jwks-rsa';
+import { ENV_CONFIG } from 'src/config';
+
+const logger = new Logger(`auth/jwks`);
+
+const client = new JwksClient({
+  jwksUri: `${ENV_CONFIG.AUTH0_M2M_TOKEN_URL}/.well-known/jwks.json`,
+  cache: true,
+  rateLimit: true,
+});
+
+/**
+ * Retrieves the signing key for a given JWT token.
+ *
+ * This function decodes the token to extract its header and uses the `kid` (Key ID)
+ * to fetch the corresponding signing key from a remote client. The signing key is
+ * then resolved as a public key.
+ *
+ * @param token - The JWT token for which the signing key is to be retrieved.
+ * @returns A promise that resolves with the public signing key as a string.
+ * @throws An error if the token is invalid, the `kid` is missing, or the signing key
+ *         cannot be retrieved or resolved.
+ */
+export const getSigningKey = (token: string) => {
+  const tokenHeader = decode(token, { complete: true })?.header;
+
+  return new Promise((resolve, reject) => {
+    if (!tokenHeader || !tokenHeader.kid) {
+      logger.error('Invalid token: Missing key ID');
+      return reject(new Error('Invalid token: Missing key ID'));
+    }
+
+    client.getSigningKey(tokenHeader.kid, function (err, key) {
+      if (err || !key) {
+        logger.error('Error getting signing key:', err);
+        return reject(new Error('Invalid token: Unable to get signing key'));
+      }
+
+      // Get the public key using the proper method
+      const signingKey = key.getPublicKey();
+
+      if (!signingKey) {
+        logger.error('Error getting public key!');
+        return reject(new Error('Invalid token: Unable to get public key'));
+      }
+
+      resolve(signingKey);
+    });
+  });
+};

src/core/auth/middleware/tokenValidator.middleware.ts

@@ -6,12 +6,13 @@ import {
 } from '@nestjs/common';
 import * as jwt from 'jsonwebtoken';
 import { ENV_CONFIG } from 'src/config';
+import { getSigningKey } from '../jwt';
 
 const logger = new Logger(`Auth/TokenValidatorMiddleware`);
 
 @Injectable()
 export class TokenValidatorMiddleware implements NestMiddleware {
-  use(req: any, res: Response, next: (error?: any) => void) {
+  async use(req: any, res: Response, next: (error?: any) => void) {
     const [type, idToken] = req.headers.authorization?.split(' ') ?? [];
 
     if (type !== 'Bearer' || !idToken) {
@@ -20,7 +21,8 @@ export class TokenValidatorMiddleware implements NestMiddleware {
 
     let decoded: any;
     try {
-      decoded = jwt.verify(idToken, ENV_CONFIG.AUTH0_CERT);
+      const signingKey = await getSigningKey(idToken);
+      decoded = jwt.verify(idToken, signingKey);
     } catch (error) {
       logger.error('Error verifying JWT', error);
       throw new UnauthorizedException('Invalid or expired JWT!');