Write python code to Build an API endpoint for role-based access control (RBAC) using Flask. accepts requests with user context; checks user roles and permissions; enforces RBAC rules; returns 403 on unauthorized. Structure the project as: app/, routes/rbac.py, models/role.py, middleware/rbac.py. Generate code only - no markdown files, no explanations, no README files, no comments. Keep output concise and purpose-ready.