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/website/models.py

@@ -0,0 +1,56 @@
+import time
+from flask_sqlalchemy import SQLAlchemy
+from authlib.integrations.sqla_oauth2 import (
+    OAuth2ClientMixin,
+    OAuth2AuthorizationCodeMixin,
+    OAuth2TokenMixin,
+)
+
+db = SQLAlchemy()
+
+
+class User(db.Model):
+    id = db.Column(db.Integer, primary_key=True)
+    username = db.Column(db.String(40), unique=True)
+
+    def __str__(self):
+        return self.username
+
+    def get_user_id(self):
+        return self.id
+
+    def check_password(self, password):
+        return password == 'valid'
+
+
+class OAuth2Client(db.Model, OAuth2ClientMixin):
+    __tablename__ = 'oauth2_client'
+
+    id = db.Column(db.Integer, primary_key=True)
+    user_id = db.Column(
+        db.Integer, db.ForeignKey('user.id', ondelete='CASCADE'))
+    user = db.relationship('User')
+
+
+class OAuth2AuthorizationCode(db.Model, OAuth2AuthorizationCodeMixin):
+    __tablename__ = 'oauth2_code'
+
+    id = db.Column(db.Integer, primary_key=True)
+    user_id = db.Column(
+        db.Integer, db.ForeignKey('user.id', ondelete='CASCADE'))
+    user = db.relationship('User')
+
+
+class OAuth2Token(db.Model, OAuth2TokenMixin):
+    __tablename__ = 'oauth2_token'
+
+    id = db.Column(db.Integer, primary_key=True)
+    user_id = db.Column(
+        db.Integer, db.ForeignKey('user.id', ondelete='CASCADE'))
+    user = db.relationship('User')
+
+    def is_refresh_token_active(self):
+        if self.revoked:
+            return False
+        expires_at = self.issued_at + self.expires_in * 2
+        return expires_at >= time.time()