From 47c4491ffc0c6ed6685257246cbe465f2b1fa3bd Mon Sep 17 00:00:00 2001
From: Filip Skokan <panva.ip@gmail.com>
Date: Thu, 9 Jan 2020 17:46:20 +0100
Subject: [PATCH] feat: detect self-issued OP and validate ID Token accordingly

---
 lib/client.js                   | 26 ++++++++++-
 test/client/self_issued.test.js | 81 +++++++++++++++++++++++++++++++++
 2 files changed, 105 insertions(+), 2 deletions(-)
 create mode 100644 test/client/self_issued.test.js

diff --git a/lib/client.js b/lib/client.js
index 46cbed5b..6aaaa696 100644
--- a/lib/client.js
+++ b/lib/client.js
@@ -800,6 +800,7 @@ module.exports = (issuer, aadIssValidation = false) => class Client extends Base
    * @api private
    */
   async validateJWT(jwt, expectedAlg, required = ['iss', 'sub', 'aud', 'exp', 'iat']) {
+    const isSelfIssued = this.issuer.issuer === 'https://self-issued.me';
     const timestamp = now();
     let header;
     let payload;
@@ -819,6 +820,10 @@ module.exports = (issuer, aadIssValidation = false) => class Client extends Base
       });
     }
 
+    if (isSelfIssued) {
+      required = [...required, 'sub_jwk']; // eslint-disable-line no-param-reassign
+    }
+
     required.forEach(verifyPresence.bind(undefined, payload, jwt));
 
     if (payload.iss !== undefined) {
@@ -907,13 +912,30 @@ module.exports = (issuer, aadIssValidation = false) => class Client extends Base
 
     let key;
 
-    if (header.alg.startsWith('HS')) {
+    if (isSelfIssued) {
+      try {
+        assert(isPlainObject(payload.sub_jwk));
+        key = jose.JWK.asKey(payload.sub_jwk);
+        assert.equal(key.type, 'public');
+      } catch (err) {
+        throw new RPError({
+          message: 'failed to use sub_jwk claim as an asymmetric JSON Web Key',
+          jwt,
+        });
+      }
+      if (key.thumbprint !== payload.sub) {
+        throw new RPError({
+          message: 'failed to match the subject with sub_jwk',
+          jwt,
+        });
+      }
+    } else if (header.alg.startsWith('HS')) {
       key = await this.joseSecret();
     } else if (header.alg !== 'none') {
       key = await this.issuer.queryKeyStore(header);
     }
 
-    if (header.alg === 'none') {
+    if (!key && header.alg === 'none') {
       return { protected: header, payload };
     }
 
diff --git a/test/client/self_issued.test.js b/test/client/self_issued.test.js
new file mode 100644
index 00000000..14b63247
--- /dev/null
+++ b/test/client/self_issued.test.js
@@ -0,0 +1,81 @@
+const { expect } = require('chai');
+const nock = require('nock');
+const timekeeper = require('timekeeper');
+const jose = require('jose');
+
+const { Issuer } = require('../../lib');
+
+const fail = () => { throw new Error('expected promise to be rejected'); };
+
+describe('Validating Self-Issued OP responses', () => {
+  afterEach(timekeeper.reset);
+  afterEach(nock.cleanAll);
+
+  before(function () {
+    const issuer = new Issuer({
+      authorization_endpoint: 'openid:',
+      issuer: 'https://self-issued.me',
+      scopes_supported: ['openid', 'profile', 'email', 'address', 'phone'],
+      response_types_supported: ['id_token'],
+      subject_types_supported: ['pairwise'],
+      id_token_signing_alg_values_supported: ['RS256'],
+      request_object_signing_alg_values_supported: ['none', 'RS256'],
+      registration_endpoint: 'https://self-issued.me/registration/1.0/',
+    });
+
+    const client = new issuer.Client({
+      client_id: 'https://rp.example.com/cb',
+      response_types: ['id_token'],
+      token_endpoint_auth_method: 'none',
+      id_token_signed_response_alg: 'ES256',
+    });
+
+    Object.assign(this, { issuer, client });
+  });
+
+  const idToken = (claims = {}) => {
+    const jwk = jose.JWK.generateSync('EC');
+    return jose.JWT.sign({
+      sub_jwk: jwk.toJWK(),
+      sub: jwk.thumbprint,
+      ...claims,
+    }, jwk, { expiresIn: '2h', issuer: 'https://self-issued.me', audience: 'https://rp.example.com/cb' });
+  };
+
+  describe('consuming an ID Token response', () => {
+    it('consumes a self-issued response', function () {
+      const { client } = this;
+      return client.callback(undefined, { id_token: idToken() });
+    });
+
+    it('expects sub_jwk to be in the ID Token claims', function () {
+      const { client } = this;
+      return client.callback(undefined, { id_token: idToken({ sub_jwk: undefined }) })
+        .then(fail, (err) => {
+          expect(err.name).to.equal('RPError');
+          expect(err.message).to.equal('missing required JWT property sub_jwk');
+          expect(err).to.have.property('jwt');
+        });
+    });
+
+    it('expects sub_jwk to be a public JWK', function () {
+      const { client } = this;
+      return client.callback(undefined, { id_token: idToken({ sub_jwk: 'foobar' }) })
+        .then(fail, (err) => {
+          expect(err.name).to.equal('RPError');
+          expect(err.message).to.equal('failed to use sub_jwk claim as an asymmetric JSON Web Key');
+          expect(err).to.have.property('jwt');
+        });
+    });
+
+    it('expects sub to be the thumbprint of the sub_jwk', function () {
+      const { client } = this;
+      return client.callback(undefined, { id_token: idToken({ sub: 'foo' }) })
+        .then(fail, (err) => {
+          expect(err.name).to.equal('RPError');
+          expect(err.message).to.equal('failed to match the subject with sub_jwk');
+          expect(err).to.have.property('jwt');
+        });
+    });
+  });
+});