Rbac Permissions Builder

---
name: rbac-permissions-builder
description: Implements role-based access control with permission matrix, route guards, policy functions, and UI permission hints. Provides middleware/guards, helper utilities, test suggestions, and permission checking patterns. Use when building "RBAC", "permissions", "access control", or "authorization".
---

# RBAC/Permissions Builder

Implement flexible role-based access control systems.

## Permission Matrix

```typescript
// Define permissions
export enum Permission {
  USER_READ = "user:read",
  USER_WRITE = "user:write",
  USER_DELETE = "user:delete",
  POST_READ = "post:read",
  POST_WRITE = "post:write",
  ADMIN_ACCESS = "admin:access",
}

// Define roles
export const ROLE_PERMISSIONS = {
  user: [Permission.USER_READ, Permission.POST_READ, Permission.POST_WRITE],
  moderator: [...userPermissions, Permission.POST_DELETE],
  admin: Object.values(Permission), // All permissions
};

// Check permission
export const hasPermission = (user: User, permission: Permission): boolean => {
  return ROLE_PERMISSIONS[user.role]?.includes(permission) ?? false;
};
```

## Route Guards (Express)

```typescript
export const requirePermission = (...permissions: Permission[]) => {
  return (req: Request, res: Response, next: NextFunction) => {
    if (!req.user) {
      return res.status(401).json({ error: "Unauthorized" });
    }

    const hasAllPermissions = permissions.every((p) =>
      hasPermission(req.user, p)
    );

    if (!hasAllPermissions) {
      return res.status(403).json({ error: "Forbidden" });
    }

    next();
  };
};

// Usage
router.delete(
  "/users/:id",
  authenticate,
  requirePermission(Permission.USER_DELETE),
  controller.delete
);
```

## Policy Pattern

```typescript
// policies/user.policy.ts
export class UserPolicy {
  static canUpdate(currentUser: User, targetUser: User): boolean {
    // Users can update themselves
    if (currentUser.id === targetUser.id) return true;

    // Admins can update anyone
    if (hasPermission(currentUser, Permission.USER_WRITE)) return true;

    return false;
  }

  static canDelete(currentUser: User, targetUser: User): boolean {
    // Can't delete yourself
    if (currentUser.id === targetUser.id) return false;

    // Only admins can delete
    return hasPermission(currentUser, Permission.USER_DELETE);
  }
}

// Usage in controller
if (!UserPolicy.canUpdate(req.user, targetUser)) {
  return res.status(403).json({ error: "Cannot update this user" });
}
```

## Resource Ownership

```typescript
export const requireOwnership = (
  getResourceUserId: (req: Request) => Promise<string>
) => {
  return async (req: Request, res: Response, next: NextFunction) => {
    const resourceUserId = await getResourceUserId(req);

    // Owner can access
    if (req.user.id === resourceUserId) {
      return next();
    }

    // Admin can access anything
    if (hasPermission(req.user, Permission.ADMIN_ACCESS)) {
      return next();
    }

    return res.status(403).json({ error: "Forbidden" });
  };
};
```

## UI Permission Hints

```typescript
// Return permissions with user
GET /api/me
{
  "user": { ... },
  "permissions": ["user:read", "post:write"]
}

// Frontend helper
export const usePermission = (permission: Permission): boolean => {
  const { user } = useAuth();
  return user?.permissions?.includes(permission) ?? false;
};

// Usage
{usePermission('user:delete') && <DeleteButton />}
```

## Best Practices

- Define permissions granularly (resource:action)
- Check at multiple layers (route, controller, UI)
- Use policies for complex rules
- Cache permission checks
- Log permission denials
- Test all permission paths

## Output Checklist

- [ ] Permission enum/constants
- [ ] Role-to-permission mapping
- [ ] Route guard middleware
- [ ] Policy classes for complex rules
- [ ] Ownership checking utilities
- [ ] Permission checking helpers
- [ ] UI permission hints endpoint
- [ ] Test cases for all permission paths