feat: Add OAuth2 server and client implementation with PKCE support

- Implemented OAuth2 server with client registration, authorization, and token endpoints.
- Created HTML templates for client authorization, client creation, and client editing.
- Developed an OAuth2 client application using Hono.js and Bun, supporting authorization code grant flow.
- Integrated PKCE (Proof Key for Code Exchange) for enhanced security during authorization.
- Added session management using cookies for user authentication.
- Included detailed README documentation for setup and usage instructions.

example-oauth2-server/app.py

@@ -0,0 +1,9 @@
+from website.app import create_app
+
+
+app = create_app({
+    'SECRET_KEY': 'secret',
+    'OAUTH2_REFRESH_TOKEN_GENERATOR': True,
+    'SQLALCHEMY_TRACK_MODIFICATIONS': False,
+    'SQLALCHEMY_DATABASE_URI': 'sqlite:///db.sqlite',
+})