Use private/public keys to sign JWTs

.gitignore

@@ -16,3 +16,6 @@ dist
 python-ldap-test*
 conf/oauth-authorization-server.json
 conf/openid-configuration.json
+conf/*.pem
+conf/*.pub
+conf/*.key

conf/config.sample.toml

@@ -25,9 +25,10 @@ USER_FILTER = "(|(uid={login})(cn={login}))"
 ADMIN_FILTER = "cn=Jane Doe"
 
 [JWT]
-KEY = "secret-key"
-ALG = "HS256"
-ISS = "http://mydomain.tld"
+PUBLIC_KEY = "conf/public.pem"
+PRIVATE_KEY = "conf/private.pem"
+KTY = "RSA"
+ALG = "RS256"
 EXP = 3600
 
 [JWT.MAPPING]

conf/openid-configuration.sample.json

@@ -9,7 +9,7 @@
     ["client_secret_basic", "private_key_jwt",
     "client_secret_post", "none"],
   "token_endpoint_auth_signing_alg_values_supported":
-    ["RS256", "ES256"],
+    ["RS256"],
   "userinfo_endpoint":
     "https://mydomain.tld/oauth/userinfo",
   "check_session_iframe":

tests/conftest.py

@@ -3,6 +3,9 @@ import ldap.ldapobject
 import os
 import pytest
 import slapdtest
+from cryptography.hazmat.primitives import serialization as crypto_serialization
+from cryptography.hazmat.primitives.asymmetric import rsa
+from cryptography.hazmat.backends import default_backend as crypto_default_backend
 from flask_webtest import TestApp
 from werkzeug.security import gen_salt
 from web import create_app
@@ -28,6 +31,37 @@ class CustomSlapdObject(slapdtest.SlapdObject):
         return config
 
 
+@pytest.fixture(scope="session")
+def keypair():
+    key = rsa.generate_private_key(
+        backend=crypto_default_backend(), public_exponent=65537, key_size=2048
+    )
+    private_key = key.private_bytes(
+        crypto_serialization.Encoding.PEM,
+        crypto_serialization.PrivateFormat.PKCS8,
+        crypto_serialization.NoEncryption(),
+    )
+    public_key = key.public_key().public_bytes(
+        crypto_serialization.Encoding.OpenSSH, crypto_serialization.PublicFormat.OpenSSH
+    )
+    return private_key, public_key
+
+
+@pytest.fixture
+def keypair_path(keypair, tmp_path):
+    private_key, public_key = keypair
+
+    private_key_path = os.path.join(tmp_path, "private.pem")
+    with open(private_key_path, "wb") as fd:
+        fd.write(private_key)
+
+    public_key_path = os.path.join(tmp_path, "public.pem")
+    with open(public_key_path, "wb") as fd:
+        fd.write(public_key)
+
+    return private_key_path, public_key_path
+
+
 @pytest.fixture(scope="session")
 def slapd_server():
     slapd = CustomSlapdObject()
@@ -75,15 +109,15 @@ def slapd_connection(slapd_server):
 
 
 @pytest.fixture
-def app(slapd_server):
+def app(slapd_server, keypair_path):
     os.environ["AUTHLIB_INSECURE_TRANSPORT"] = "true"
+    private_key_path, public_key_path = keypair_path
 
     app = create_app(
         {
             "SECRET_KEY": gen_salt(24),
             "OAUTH2_METADATA_FILE": "conf/oauth-authorization-server.sample.json",
             "OIDC_METADATA_FILE": "conf/openid-configuration.sample.json",
-
             "LDAP": {
                 "ROOT_DN": slapd_server.suffix,
                 "URI": slapd_server.ldap_uri,
@@ -93,9 +127,10 @@ def app(slapd_server):
                 "ADMIN_FILTER": "uid=admin",
             },
             "JWT": {
-                "KEY": "secret-key",
-                "ALG": "HS256",
-                "ISS": "https://mydomain.tld",
+                "PUBLIC_KEY": public_key_path,
+                "PRIVATE_KEY": private_key_path,
+                "ALG": "RS256",
+                "KTY": "RSA",
                 "EXP": 3600,
                 "MAPPING": {
                     "SUB": "uid",

tests/test_hybrid_flow.py

@@ -42,7 +42,7 @@ def test_oauth_hybrid(testclient, slapd_connection, user, client):
     assert {"foo": "bar"} == res.json
 
 
-def test_oidc_hybrid(testclient, slapd_connection, logged_user, client):
+def test_oidc_hybrid(testclient, slapd_connection, logged_user, client, keypair):
     res = testclient.get(
         "/oauth/authorize",
         params=dict(
@@ -69,7 +69,7 @@ def test_oidc_hybrid(testclient, slapd_connection, logged_user, client):
     assert token is not None
 
     id_token = params["id_token"][0]
-    claims = jwt.decode(id_token, "secret-key")
+    claims = jwt.decode(id_token, keypair[1])
     assert logged_user.uid[0] == claims["sub"]
     assert logged_user.cn[0] == claims["name"]
     assert [client.oauthClientID] == claims["aud"]

tests/test_implicit_flow.py

@@ -47,7 +47,7 @@ def test_oauth_implicit(testclient, slapd_connection, user, client):
     client.save(slapd_connection)
 
 
-def test_oidc_implicit(testclient, slapd_connection, user, client):
+def test_oidc_implicit(testclient, keypair, slapd_connection, user, client):
     client.oauthGrantType = ["token id_token"]
     client.oauthTokenEndpointAuthMethod = "none"
 
@@ -83,7 +83,7 @@ def test_oidc_implicit(testclient, slapd_connection, user, client):
     assert token is not None
 
     id_token = params["id_token"][0]
-    claims = jwt.decode(id_token, "secret-key")
+    claims = jwt.decode(id_token, keypair[1])
     assert user.uid[0] == claims["sub"]
     assert user.cn[0] == claims["name"]
     assert [client.oauthClientID] == claims["aud"]

web/oauth.py

@@ -1,4 +1,4 @@
-from authlib.common.encoding import urlsafe_b64encode
+from authlib.jose import jwk
 from authlib.oauth2 import OAuth2Error
 from flask import Blueprint, request, session, redirect
 from flask import render_template, jsonify, flash, current_app
@@ -71,8 +71,19 @@ def revoke_token():
 
 @bp.route("/jwks.json")
 def jwks():
-    # TODO: Do not share secrets here!
-    key = urlsafe_b64encode(current_app.config["JWT"]["KEY"].encode("utf-8")).decode(
-        "utf-8"
+    with open(current_app.config["JWT"]["PUBLIC_KEY"]) as fd:
+        pubkey = fd.read()
+
+    obj = jwk.dumps(pubkey, current_app.config["JWT"]["KTY"])
+    return jsonify(
+        {
+            "keys": [
+                {
+                    "kid": None,
+                    "use": "sig",
+                    "alg": current_app.config["JWT"]["ALG"],
+                    **obj,
+                }
+            ]
+        }
     )
-    return jsonify({"keys": [{"kid": None, "kty": "oct", "k": key}]})

web/oauth2utils.py

@@ -28,12 +28,13 @@ def exists_nonce(nonce, req):
 
 
 def get_jwt_config(grant):
-    return {
-        "key": current_app.config["JWT"]["KEY"],
-        "alg": current_app.config["JWT"]["ALG"],
-        "iss": current_app.config["JWT"]["ISS"],
-        "exp": current_app.config["JWT"]["EXP"],
-    }
+    with open(current_app.config["JWT"]["PRIVATE_KEY"]) as pk:
+        return {
+            "key": pk.read(),
+            "alg": current_app.config["JWT"]["ALG"],
+            "iss": authorization.metadata["issuer"],
+            "exp": current_app.config["JWT"]["EXP"],
+        }
 
 
 def generate_user_info(user, scope):
@@ -253,7 +254,7 @@ class IntrospectionEndpoint(_IntrospectionEndpoint):
             "scope": token.get_scope(),
             "sub": token.oauthSubject,
             "aud": token.oauthClientID,
-            "iss": current_app.config["JWT"]["ISS"],
+            "iss": authorization.metadata["issuer"],
             "exp": token.get_expires_at(),
             "iat": token.get_issued_at(),
         }