From 945c70b238ec3cc31613b3c17d5ad57c5a2eedee Mon Sep 17 00:00:00 2001
From: Frederick Muriuki Muriithi
Date: Thu, 18 Jul 2024 16:43:17 -0500
Subject: Retrieve newest JWK, creating a new JWK where necessary.

To help with key rotation, we fetch the latest key, creating a new JWK
in any of the following 2 conditions:
* There is no JWK in the first place
* The "newest" key is older than a specified number of days
---
 gn_auth/auth/authentication/oauth2/server.py | 43 +++++++++++++++++++++-------
 gn_auth/settings.py                          |  2 ++
 2 files changed, 35 insertions(+), 10 deletions(-)

diff --git a/gn_auth/auth/authentication/oauth2/server.py b/gn_auth/auth/authentication/oauth2/server.py
index d845c60..d1aa69e 100644
--- a/gn_auth/auth/authentication/oauth2/server.py
+++ b/gn_auth/auth/authentication/oauth2/server.py
@@ -1,15 +1,20 @@
 """Initialise the OAuth2 Server"""
+import os
 import uuid
-import datetime
+from pathlib import Path
 from typing import Callable
+from datetime import datetime, timedelta
 
+from pymonad.either import Left
 from flask import Flask, current_app
-from authlib.jose import jwk, jwt
 from authlib.oauth2.rfc7523 import JWTBearerTokenValidator
+from authlib.jose import jwk, jwt, JsonWebKey
 from authlib.oauth2.rfc6749.errors import InvalidClientError
 from authlib.integrations.flask_oauth2 import AuthorizationServer
 
 from gn_auth.auth.db import sqlite3 as db
+from gn_auth.auth.jwks import (
+    newest_jwk, jwks_directory, generate_and_save_private_key)
 
 from .models.oauth2client import client as fetch_client
 from .models.oauth2token import OAuth2Token, save_token
@@ -86,10 +91,25 @@ def create_save_token_func(token_model: type, jwtkey: jwk) -> Callable:
 
     return __save_token__
 
+def newest_jwk_with_rotation(jwksdir: Path, keyage: int) -> JsonWebKey:
+    """
+    Retrieve the latests JWK, creating a new one if older than `keyage` days.
+    """
+    def newer_than_days(jwkey):
+        filestat = os.stat(Path(
+            jwksdir, f"{jwkey.as_dict()['kid']}.private.pem"))
+        oldesttimeallowed = (datetime.now() - timedelta(days=keyage))
+        if filestat.st_ctime < (oldesttimeallowed.timestamp()):
+            return Left("JWK is too old!")
+        return jwkey
+
+    return newest_jwk(jwksdir).then(newer_than_days).either(
+        lambda _errmsg: generate_and_save_private_key(jwksdir),
+        lambda key: key)
+
 
 def make_jwt_token_generator(app):
     """Make token generator function."""
-    _gen = JWTBearerTokenGenerator(app.config["SSL_PRIVATE_KEY"])
     def __generator__(# pylint: disable=[too-many-arguments]
             grant_type,
             client,
@@ -98,13 +118,16 @@ def make_jwt_token_generator(app):
             expires_in=None,# pylint: disable=[unused-argument]
             include_refresh_token=True
     ):
-        return _gen.__call__(
-            grant_type,
-            client,
-            user,
-            scope,
-            JWTBearerTokenGenerator.DEFAULT_EXPIRES_IN,
-            include_refresh_token)
+        return JWTBearerTokenGenerator(
+            newest_jwk_with_rotation(
+                jwks_directory(app),
+                int(app.config["JWKS_ROTATION_AGE_DAYS"]))).__call__(
+                        grant_type,
+                        client,
+                        user,
+                        scope,
+                        JWTBearerTokenGenerator.DEFAULT_EXPIRES_IN,
+                        include_refresh_token)
     return __generator__
 
 
diff --git a/gn_auth/settings.py b/gn_auth/settings.py
index 7dc0105..ab6b079 100644
--- a/gn_auth/settings.py
+++ b/gn_auth/settings.py
@@ -32,6 +32,8 @@ CORS_HEADERS = [
 # OpenSSL keys
 CLIENTS_SSL_PUBLIC_KEYS_DIR = "" # clients' public keys' directory
 SSL_PRIVATE_KEY = "" # authorisation server primary key
+JWKS_ROTATION_AGE_DAYS = 7 # Days (from creation) to keep a JWK in use.
+JWKS_DELETION_AGE_DAYS = 14 # Days (from creation) to keep a JWK around before deleting it.
 
 ## Email
 SMTP_HOST = "smtp.genenetwork.org" # does not actually exist right now
-- 
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