feat(jwe): decrypt JWE-encrypted access tokens

Decrypt JWE-encrypted access tokens before writing them to the session, at
both the callback and on token refresh, so req.oidc.accessToken and
afterCallback always receive a plaintext JWT. Enabled by setting
accessTokenDecryptionKey. The key-management algorithm is read from the JWE
header and validated against a strong-algorithm allowlist; accessTokenDecryptionAlg
can pin it. Decryption failures surface a clear error.

Author: jd3vi1

EXAMPLES.md

@@ -15,6 +15,7 @@
 13. [Use a proxy for OIDC requests](#13-use-a-proxy-for-oidc-requests)
 14. [Session expiry from upstream IdP (IPSIE `session_expiry`)](#14-session-expiry-from-upstream-idp-ipsie-session_expiry)
 15. [JWT-Secured Authorization Requests (JAR)](#15-jwt-secured-authorization-requests-jar)
+16. [Decrypt JWE-encrypted access tokens](#16-decrypt-jwe-encrypted-access-tokens)
 
 ## 1. Basic setup
 
@@ -567,3 +568,28 @@ app.use(
 The request object's `aud` is set to the issuer identifier advertised in the discovery document (which may differ from `issuerBaseURL`, e.g. a trailing slash), as JAR requires. `requestObjectSigningKey` accepts the same key formats as `clientAssertionSigningKey` (PEM string, Buffer, KeyObject, JWK, CryptoKey).
 
 Full example at [jar.js](./examples/jar.js), to run it: `npm run start:example -- jar`
+
+## 16. Decrypt JWE-encrypted access tokens
+
+When an Auth0 API is configured with [Token Encryption](https://auth0.com/docs/secure/tokens/access-tokens/json-web-encryption), the access token returned at the callback is a JWE. Set `accessTokenDecryptionKey` and the SDK decrypts it before writing it to the session, at both the callback and on token refresh, so `req.oidc.accessToken` and `afterCallback` always receive a plaintext JWT. No change is needed in consuming code.
+
+```js
+app.use(
+  auth({
+    authorizationParams: {
+      response_type: 'code', // requires a client secret; JWE requires a code flow
+      audience: 'https://your-api/',
+      scope: 'openid profile email offline_access',
+    },
+    // Private key matching the public key uploaded to the API's Token Encryption
+    // settings. Accepts PEM string, Buffer, KeyObject, JWK, or CryptoKey.
+    accessTokenDecryptionKey: fs.readFileSync('./api-decryption-key.pem'),
+    // Optional pin. Omit to auto-detect the algorithm from the JWE header.
+    // accessTokenDecryptionAlg: 'RSA-OAEP-512',
+  }),
+);
+```
+
+The key-management algorithm is read from the JWE protected header (validated against a strong-algorithm allowlist), so decryption works whether the tenant uses `RSA-OAEP-256`, `RSA-OAEP-512`, and so on. Set `accessTokenDecryptionAlg` only if you want to pin one. Decryption requires a code flow, since implicit flow does not return access tokens from the token endpoint.
+
+Full example at [jwe.js](./examples/jwe.js).

examples/jwe.js

@@ -0,0 +1,58 @@
+const express = require('express');
+const { auth } = require('../');
+
+const app = express();
+
+// JWE access token decryption demo.
+//
+// When Auth0 is configured to encrypt access tokens for an API (Dashboard > APIs >
+// your API > Token Encryption), the token returned at the callback is a JWE (five
+// dot-separated parts). With `accessTokenDecryptionKey` set, the SDK decrypts it
+// before writing it to the session - at both the callback and on token refresh -
+// so `req.oidc.accessToken` and `afterCallback` always see a plaintext JWT.
+//
+// The key-management algorithm is read from the JWE protected header (validated
+// against a strong-alg allowlist), so decryption works whether the tenant uses
+// RSA-OAEP-256, RSA-OAEP-512, etc. Set `accessTokenDecryptionAlg` only to pin one.
+//
+// Requires a code flow and an API that encrypts tokens, so this example is not
+// runnable against the mock provider (it does not encrypt). It shows the config.
+
+app.use(
+  auth({
+    authRequired: false,
+    clientSecret: '__your_client_secret__',
+    authorizationParams: {
+      response_type: 'code',
+      // Request the API whose access tokens are encrypted.
+      audience: 'https://your-api/',
+      scope: 'openid profile email offline_access',
+    },
+
+    // Private key matching the public key uploaded to the API's Token Encryption
+    // settings. Accepts PEM string, Buffer, KeyObject, JWK, or CryptoKey.
+    accessTokenDecryptionKey: require('fs').readFileSync(
+      './api-decryption-key.pem',
+    ),
+    // Optional pin. Omit to auto-detect the alg from the JWE header.
+    // accessTokenDecryptionAlg: 'RSA-OAEP-512',
+  }),
+);
+
+app.get('/', (req, res) => {
+  if (req.oidc.isAuthenticated()) {
+    const token = req.oidc.accessToken?.access_token;
+    // A decrypted token is a normal 3-part JWT; a 5-part value means it is still
+    // encrypted (decryption key not active).
+    const parts = token ? token.split('.').length : 0;
+    res.send(
+      `<p>Logged in as <strong>${req.oidc.user.sub}</strong></p>` +
+        `<p>Access token parts: ${parts} (3 = decrypted JWT)</p>` +
+        `<a href="/logout">logout</a>`,
+    );
+  } else {
+    res.send('<a href="/login">login</a>');
+  }
+});
+
+module.exports = app;

index.d.ts

@@ -847,6 +847,22 @@ interface ConfigParams {
    */
   requestObjectSigningKeyId?: string;
 
+  /**
+   * Private key used to decrypt JWE-encrypted access tokens.
+   * When set, the SDK decrypts the access token at the callback and on refresh
+   * before writing it to the session, so `req.oidc.accessToken` and `afterCallback`
+   * always receive a plaintext JWT. Requires a code flow (`response_type: 'code'`
+   * or `'code id_token'`). Accepts PEM string, Buffer, KeyObject, JWK, or CryptoKey.
+   */
+  accessTokenDecryptionKey?: KeyObject | JoseCryptoKey | JWK | string | Buffer;
+
+  /**
+   * Optional pin for the JWE key-management algorithm. When omitted, the algorithm
+   * is read from the JWE protected header (validated against a strong-algorithm
+   * allowlist), so decryption works with whatever alg the tenant uses.
+   */
+  accessTokenDecryptionAlg?: string;
+
   /**
    * Additional request body properties to be sent to the `token_endpoint` during authorization code exchange or token refresh.
    */

index.test-d.ts

@@ -15,3 +15,11 @@ expectType<RequestHandler>(
     requestObjectSigningKeyId: 'kid-1',
   }),
 );
+
+// JWE access token decryption
+expectType<RequestHandler>(
+  auth({
+    accessTokenDecryptionKey: '-----BEGIN PRIVATE KEY-----',
+    accessTokenDecryptionAlg: 'RSA-OAEP-512',
+  }),
+);

lib/client.js

@@ -1,6 +1,12 @@
 const crypto = require('crypto');
 const client = require('openid-client');
-const { importPKCS8, importJWK, exportPKCS8, SignJWT } = require('jose');
+const {
+  importPKCS8,
+  importJWK,
+  exportPKCS8,
+  SignJWT,
+  compactDecrypt,
+} = require('jose');
 const pkg = require('../package.json');
 const debug = require('./debug')('client');
 
@@ -308,7 +314,45 @@ async function buildRequestObject(authParams, config, audience) {
     .sign(key);
 }
 
+// Key-management ("alg") algorithms accepted for access-token decryption when the
+// developer has not pinned one. Deliberately excludes RSA1_5 (PKCS#1 v1.5), which
+// is vulnerable to Bleichenbacher padding-oracle attacks. jose enforces this list
+// against the JWE header before the key is imported, so a token cannot downgrade
+// us to a weak or unexpected algorithm.
+const ALLOWED_ACCESS_TOKEN_JWE_ALGS = [
+  'RSA-OAEP',
+  'RSA-OAEP-256',
+  'RSA-OAEP-384',
+  'RSA-OAEP-512',
+  'ECDH-ES',
+  'ECDH-ES+A128KW',
+  'ECDH-ES+A192KW',
+  'ECDH-ES+A256KW',
+];
+
+/**
+ * Decrypts a JWE-encrypted access token.
+ * Co-located here so it can call the internal importPrivateKey helper directly.
+ *
+ * The key-management algorithm is taken from the JWE protected header (so the tenant
+ * can encrypt with e.g. RSA-OAEP-256 or RSA-OAEP-512 without the client pre-declaring
+ * it) but ONLY after jose validates it against an allowlist of strong algorithms.
+ * This prevents algorithm-confusion / downgrade attacks (notably RSA1_5). When the
+ * developer sets `accessTokenDecryptionAlg`, the allowlist is narrowed to that one
+ * value, turning it into a hard pin.
+ */
+async function decryptAccessToken(token, keyData, alg) {
+  const keyManagementAlgorithms = alg ? [alg] : ALLOWED_ACCESS_TOKEN_JWE_ALGS;
+  const { plaintext } = await compactDecrypt(
+    token,
+    (header) => importPrivateKey(keyData, header.alg),
+    { keyManagementAlgorithms },
+  );
+  return Buffer.from(plaintext).toString('utf8');
+}
+
 exports.buildRequestObject = buildRequestObject;
+exports.decryptAccessToken = decryptAccessToken;
 
 exports.get = (config) => {
   const { discoveryCacheMaxAge: cacheMaxAge } = config;

lib/config.js

@@ -371,6 +371,24 @@ const paramsSchema = Joi.object({
       otherwise: Joi.string().optional(),
     }),
   requestObjectSigningKeyId: Joi.string().optional(),
+  accessTokenDecryptionKey: Joi.any()
+    .optional()
+    .when(
+      Joi.ref('authorizationParams.response_type', {
+        adjust: (v) => v && !v.includes('code'),
+      }),
+      {
+        is: true,
+        then: Joi.any().forbidden().messages({
+          'any.unknown':
+            '"accessTokenDecryptionKey" requires a code flow. Set authorizationParams.response_type to "code" or "code id_token".',
+        }),
+      },
+    ),
+  // Optional pin. When omitted, the key-management alg is read from the JWE
+  // protected header, so decryption works with whatever alg the tenant uses
+  // (e.g. RSA-OAEP-256 or RSA-OAEP-512). When set, the token's alg must match.
+  accessTokenDecryptionAlg: Joi.string().optional(),
   discoveryCacheMaxAge: Joi.number()
     .optional()
     .min(0)

lib/context.js

@@ -18,6 +18,7 @@ const {
   get: getClient,
   buildEndSessionUrl,
   buildRequestObject,
+  decryptAccessToken,
   client: oidcClient,
 } = require('./client');
 const { encodeState, decodeState } = require('../lib/hooks/getLoginState');
@@ -224,11 +225,34 @@ async function refresh({ tokenEndpointParams } = {}) {
     parameters,
   );
 
+  // Decrypt the refreshed access token when JWE decryption is configured, so the
+  // stored token and req.oidc.accessToken remain plaintext JWTs after a refresh —
+  // consistent with the callback. Without this, encrypted tokens would revert to
+  // ciphertext on the first refresh.
+  let refreshedAccessToken = newTokenSet.access_token;
+  if (config.accessTokenDecryptionKey && refreshedAccessToken) {
+    try {
+      refreshedAccessToken = await decryptAccessToken(
+        refreshedAccessToken,
+        config.accessTokenDecryptionKey,
+        config.accessTokenDecryptionAlg,
+      );
+    } catch (error) {
+      throw createError(
+        500,
+        `Failed to decrypt the refreshed access token: ${error.message}. ` +
+          'Check that accessTokenDecryptionKey matches the key configured on the ' +
+          'authorization server, and that accessTokenDecryptionAlg (if set) matches ' +
+          'the JWE "alg".',
+      );
+    }
+  }
+
   // Update the session, preserving sessionExpiresAt — the refresh-token grant
   // does not return a session_expiry claim, so we must not overwrite the ceiling
   // that was set at login.
   Object.assign(session, {
-    access_token: newTokenSet.access_token,
+    access_token: refreshedAccessToken,
     // If no new ID token assume the current ID token is valid.
     id_token: newTokenSet.id_token || oldTokenSet.id_token,
     // If no new refresh token assume the current refresh token is valid.
@@ -852,6 +876,28 @@ class ResponseContext {
           : undefined,
       };
 
+      if (config.accessTokenDecryptionKey && session.access_token) {
+        try {
+          session.access_token = await decryptAccessToken(
+            session.access_token,
+            config.accessTokenDecryptionKey,
+            config.accessTokenDecryptionAlg,
+          );
+        } catch (error) {
+          // Surface a clear, actionable error instead of a raw crypto stack trace.
+          // The most common causes are a key that does not match the tenant's
+          // encryption key, or an accessTokenDecryptionAlg that does not match the
+          // alg the token was encrypted with.
+          throw createError(
+            500,
+            `Failed to decrypt the access token: ${error.message}. ` +
+              'Check that accessTokenDecryptionKey matches the key configured on the ' +
+              'authorization server, and that accessTokenDecryptionAlg (if set) matches ' +
+              'the JWE "alg".',
+          );
+        }
+      }
+
       // Must store the `sid` separately as the ID Token gets overridden by
       // ID Token from the Refresh Grant which may not contain a sid (In Auth0 currently).
       session.sid = claims?.sid;