Permission Gate

# Permission Gate

Enforce access control in code, not prompts.

## Category
Tool Security

## Context
Tools with varying access levels.

## Problem
Prompt-based restrictions can be bypassed. Code must enforce rules.

## Solution
Enforce in code:
- **Check permissions**: Before executing
- **Principle of least privilege**: Minimum needed
- **Audit denials**: Log for security review
- **Clear errors**: Explain what's denied

## Example (Python)
```python
@tool
def delete_user(
    context: Context,
    user_id: str
) -> DeleteResult:
    """Delete a user. Requires admin role."""
    # Enforce in code, not prompt
    if "admin" not in context.user.roles:
        raise PermissionDenied(
            action="delete_user",
            required_role="admin",
            user_roles=context.user.roles
        )
    
    # Also check if they can delete THIS user
    if not can_delete(context.user, user_id):
        raise PermissionDenied(
            action="delete_user",
            reason="Cannot delete users outside your organization"
        )
    
    return users_api.delete(user_id)
```

## Considerations
- Never trust prompt-based restrictions
- Check permissions at the start of execution
- Log all permission denials

## Related Patterns
- secret-injection
- audit-trail
- identity-anchor

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Source: https://arcade.dev/patterns/permission-gate