Add comprehensive documentation for LeagueLedger

- Created architecture overview in development/architecture.md
- Added installation guide in getting-started/installation.md
- Developed user guide with detailed instructions in user-guide/overview.md, user-guide/teams.md, user-guide/qr-codes.md
- Implemented social login setup documentation in social_login_setup.md
- Updated index.md to include links to new documentation sections
- Configured mkdocs.yml for site structure and theme
- Added requirements.txt for documentation dependencies

app/auth/middleware.py

@@ -0,0 +1,74 @@
+from starlette.authentication import (
+    AuthCredentials, AuthenticationBackend, UnauthenticatedUser
+)
+from sqlalchemy.orm import Session
+from ..db import SessionLocal
+from ..models import User
+
+class SessionAuthBackend(AuthenticationBackend):
+    """
+    Authentication backend that uses session data to authenticate users.
+    This maintains compatibility with the existing session-based authentication
+    while providing the structure of Starlette's authentication system.
+    """
+    
+    async def authenticate(self, request):
+        """
+        Authenticate the user from the session.
+        
+        Args:
+            request: The FastAPI/Starlette request object.
+            
+        Returns:
+            Tuple of (AuthCredentials, User) if authenticated,
+            or None if not authenticated.
+        """
+        # Check for user_id in session
+        user_id = request.session.get("user_id")
+        if not user_id:
+            # Return None to indicate no authentication
+            return None
+            
+        # Get database connection
+        db = SessionLocal()
+        try:
+            # Fetch user from database
+            user = db.query(User).filter(User.id == user_id).first()
+            
+            # If user exists, set credentials and return user
+            if user:
+                # Base credentials for all authenticated users
+                scopes = ["authenticated"]
+                
+                # Add admin scope if user is admin
+                if user.is_admin:
+                    scopes.append("admin")
+                    
+                # Add verified scope if user is verified
+                if user.is_verified:
+                    scopes.append("verified")
+                
+                # Add OAuth provider scope if it exists
+                # This allows policies to be set based on authentication source
+                oauth_provider = request.session.get("oauth_provider")
+                if oauth_provider:
+                    scopes.append(f"oauth:{oauth_provider}")
+                
+                # Return credentials and user
+                return AuthCredentials(scopes), user
+        finally:
+            db.close()
+        
+        # If we get here, user not found but session exists
+        # Clear session on next request (handled in middleware)
+        return None
+
+def on_auth_error(request, exc):
+    """Handle authentication errors by redirecting to login"""
+    from fastapi.responses import RedirectResponse
+    
+    # Build the redirect URL with the original requested path as 'next'
+    login_url = f"/auth/login?next={request.url.path}"
+    
+    # Return redirect response
+    return RedirectResponse(url=login_url, status_code=303)