# 05 — Auth: Users Service + Role-Gated UI

**Goal:**  
- Require login for certain actions.  
- Show/hide UI components based on user role.  
- Gate sensitive server functions so only specific roles can run them.

---

## 1) What You’ll Build
- A login/logout button set.
- UI elements that only appear for specific roles (`editor`, `admin`).
- A server callable (`dangerous_action`) that only certain roles can call.
- Friendly messages when a user tries to overstep their privileges.

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## 2) Enable the Users Service
In your Anvil app:
1. **App → Settings → Users Service → Enable**.
2. Add a few test users in the Users table:
   - Columns: `email`, `password`, `roles` (Text, Comma-separated, e.g., `editor`, `admin`).
3. Assign roles for each user. Example:
   - `alice@example.com` → roles: `editor`
   - `bob@example.com` → roles: `viewer`
   - `root@example.com` → roles: `admin`

---

## 3) Server-Side Role Helper
Add to `ServerModule1` (or create `auth_helpers.py` if you prefer):

```python
import anvil.server
import anvil.users

def require_role(*roles):
    """
    Ensure the logged-in user has at least one of the given roles.
    """
    user = anvil.users.get_user()
    if not user:
        raise PermissionError("You must be logged in.")
    user_roles = set((user.get('roles') or "").replace(" ", "").split(","))
    if not set(roles).intersection(user_roles):
        raise PermissionError(f"You need one of these roles: {', '.join(roles)}")

@anvil.server.callable
def dangerous_action():
    """
    Only 'editor' or 'admin' can run this.
    """
    require_role('editor', 'admin')
    return "Sensitive operation completed successfully."
````

---

## 4) Client UI Setup

On `Form1`:

* Add two Buttons:

  * `button_login` → text: “Login”
  * `button_logout` → text: “Logout”
* Add a Label: `label_user_info` (for current user/roles).
* Add a Button: `button_danger` → text: “Run Dangerous Action” (editor/admin only).
* Arrange them neatly in a ColumnPanel or RowPanel.

---

## 5) Client Code (Form1)

```python
from anvil import *
import anvil.server
import anvil.users

class Form1(Form1Template):

    def __init__(self, **properties):
        self.init_components(**properties)
        self.refresh_ui()

    def refresh_ui(self):
        """Refreshes UI based on login status and roles."""
        user = anvil.users.get_user()
        if user:
            roles = (user.get('roles') or "").replace(" ", "")
            self.label_user_info.text = f"Logged in as: {user['email']} ({roles})"
            self.button_login.visible = False
            self.button_logout.visible = True
            # Show dangerous button only if editor/admin
            role_list = roles.split(",")
            self.button_danger.visible = any(r in ('editor', 'admin') for r in role_list)
        else:
            self.label_user_info.text = "Not logged in"
            self.button_login.visible = True
            self.button_logout.visible = False
            self.button_danger.visible = False

    def button_login_click(self, **event_args):
        """Log the user in."""
        anvil.users.login_with_form()
        self.refresh_ui()

    def button_logout_click(self, **event_args):
        """Log the user out."""
        anvil.users.logout()
        self.refresh_ui()

    def button_danger_click(self, **event_args):
        """Attempt to run the dangerous action."""
        try:
            res = anvil.server.call('dangerous_action')
            Notification(res, style='success', timeout=3).show()
        except PermissionError as e:
            Notification(str(e), style='danger', timeout=3).show()
        except Exception as e:
            Notification(f"Error: {e}", style='danger').show()
```

---

## 6) Test Scenarios

1. **Not logged in** → No dangerous button visible; clicking login prompts login form.
2. **Logged in as viewer** → Sees dangerous button hidden.
3. **Logged in as editor/admin** → Sees dangerous button; clicking it runs `dangerous_action` and shows success message.
4. **Force test**: Temporarily show dangerous button for all roles, click it as a viewer, verify server rejects with `PermissionError`.

---

## 7) Bonus: Role Badge

* Add a Label next to `label_user_info` styled with a background color based on role.
* Example: `editor` → blue badge, `admin` → red badge.

---

## 8) Demo Asset

Record a short GIF showing:

1. Logging in as viewer → no dangerous button.
2. Logging in as editor → dangerous button appears and works.
3. Logging in as admin → same, but maybe with admin-only UI section.

Save as: `/assets/auth-roles-demo.gif`

Reference in this tutorial:

```markdown
![Auth Roles Demo](../assets/auth-roles-demo.gif)
```

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## 9) Takeaways

* Roles allow fine-grained control without changing client code.
* Always check roles **server-side** — the client can be modified by anyone.
* Hide UI for UX; enforce on server for security.

---