---
title: Authentication in Nexios
description: Secure your API with just one line of code!
head:
  - - meta
    - property: og:title
      content: Authentication in Nexios
  - - meta
    - property: og:description
      content: Secure your API with just one line of code!
---

# Authentication in Nexios

**Secure your API with just one line of code!**

Nexios makes authentication simple yet powerful. Here's all you need to get started:

::: code-group

```python [Simple Example]
from nexios import NexiosApp
from nexios.http import Request, Response
from nexios.auth.decorators import auth

app = NexiosApp()

@app.get("/public")
async def public_data(request: Request, response: Response):
    return {"message": "Hello, world!"}

@app.get("/profile")
@auth()
async def user_profile(request: Request, response: Response):
    return {
        "message": f"Welcome back, {request.user.display_name}!",
        "user_id": request.user.identity,
        "is_authenticated": request.user.is_authenticated
    }
```

```python [Scope Specific]
from nexios import NexiosApp
from nexios.auth.decorators import auth

app = NexiosApp()

@app.get("/admin/dashboard")
@auth(["jwt"])
async def admin_dashboard(request: Request, response: Response):
    return {
        "message": "Admin access granted",
        "admin_features": ["user_management", "analytics", "settings"]
    }
```

```python [With Authorization]
from nexios import NexiosApp
from nexios.auth.decorators import has_permission

app = NexiosApp()

@app.get("/api/secure-data")
@has_permission("api.read")
async def secure_data(request: Request, response: Response):
    return {"data": "Ultra-secure data!"}
```

:::

### Key Features at a Glance

- **One-line protection**: Just add `@auth()` to secure any route
- **Multiple auth methods**: JWT, Session, API Key, or bring your own
- **Role-based access control**: Easily implement user permissions
- **Built-in security**: Protection against common web vulnerabilities
- **Flexible & extensible**: Customize to fit any use case

## Authentication Middleware

The `AuthenticationMiddleware` is the core component that handles authentication for incoming requests. It processes each request, extracts authentication credentials, and attaches user information to the request object.

### Basic Configuration

```python
from nexios.auth.middleware import AuthenticationMiddleware
from nexios.auth.backends.jwt import JWTAuthBackend

# Configure JWT backend
jwt_backend = JWTAuthBackend(
    authenticate_func=load_user_from_jwt
)

# Add to middleware
app.add_middleware(AuthenticationMiddleware(backend=jwt_backend))
```

::: tip
the `authenticate_func` is responible to get the user from the decoded payload which is provided from the backend , and what ever is retuended by the function is what will be used as request.jwt.
:::

## Built-in User Classes

Nexios provides several built-in user classes that you can use or extend for your authentication needs.

### BaseUser

The abstract base class that defines the interface all user objects must implement.

```python
from nexios.auth.base import BaseUser

class CustomUser(BaseUser):
    @property
    def is_authenticated(self) -> bool:
        return True  # Implement authentication check

    @property
    def display_name(self) -> str:
        return "User Display Name"  # Implement display name

    @property
    def identity(self) -> str:
        return "user123"  # Implement unique identifier
```

**Key Methods:**

- `is_authenticated`: Returns `True` if the user is authenticated
- `display_name`: Returns a human-readable name for the user
- `identity`: Returns a unique identifier for the user

### SimpleUser

A concrete implementation of `BaseUser` for basic authentication needs.

```python
from nexios.auth.base import SimpleUser

# Create an authenticated user
user = SimpleUser(username="john_doe")
print(user.is_authenticated)  # True
print(user.display_name)     # "john_doe"
print(user.identity)         # "john_doe"
```

**Features:**

- Simple constructor that takes just a username
- Implements all required `BaseUser` methods
- `identity` defaults to the username
- `is_authenticated` is always `True`

### UnauthenticatedUser

Represents an unauthenticated user (returned when authentication fails).

```python
from nexios.auth.base import UnauthenticatedUser

user = UnauthenticatedUser()
print(user.is_authenticated)  # False
print(user.display_name)     # ""
print(user.identity)         # ""
```

### Using in authenticate_func

The above user management classes should be used in the `authenticate_func` of an authentication backend. For example, using the `SimpleUser` class with the `SessionAuthBackend` class:

```python
from nexios.auth.backends.session import SessionAuthBackend
from nexios.auth.base import SimpleUser

async def load_user_from_session(**session_data: dict) -> SimpleUser:
    """Load user from session data"""
    if "user" in session_data:
        return SimpleUser(username=session_data["user"]["username"])
    return None

session_backend = SessionAuthBackend(
    authenticate_func=load_user_from_session,
    user_key="user"  # Key in session where user data is stored
)
```

::: tip
the `authenticate_func` for `SessionAuthBackend` and `JWTAuthBackend` should take a mapping of the session data as a keyword argument
:::

## Fine-Grained Permission Control

Nexios provides a flexible permission system that works with both the built-in `SimpleUser` class and custom user classes that cab inherit from `BaseUser`. The `has_permission` decorator integrates with this system to control access to your routes.

### Using SimpleUser for Basic Permissions

For simple applications, you can use the built-in `SimpleUser` class which provides basic permission checking:

```python
from nexios.auth.base import SimpleUser


# Example with authenticate_func in authbackend
async def authenticate_func(*args, **kwargs) -> SimpleUser:
    """Authenticate user with username and password"""
    # Implement your authentication logic here

    return SimpleUser(
        username="editor",
        permissions=["content.edit", "content.view"]
    )

# In your route handler
@app.get("/content")
@has_permission("content.view")  # User must have this permission
async def view_content(request, response):
    # Since we passed the permission check, we know the user has "content.view"
    return {"content": "This is protected content"}
```

### Creating Custom User Classes with BaseUser

For more complex permission logic, create a custom user class by subclassing `BaseUser`:

```python
from nexios.auth.base import BaseUser

class CustomUser(BaseUser):
    def __init__(self, username: str, roles: list):
        self.username = username
        self.roles = roles
        self._permissions = self._load_permissions()

    def _load_permissions(self):
        permissions = set()
        if "admin" in self.roles:
            permissions.add("*")
        if "editor" in self.roles:
            permissions.update(["content.edit", "content.view"])
        return permissions

    @property
    def is_authenticated(self) -> bool:
        return True  # This user is always authenticated

    @property
    def display_name(self) -> str:
        return self.username

    @property
    def identity(self) -> str:
        return self.username

    def has_permission(self, permission: str) -> bool:
        return "*" in self._permissions or permission in self._permissions


```

**Check permissions conditionally**:

```python
@app.get("/content/<content_id>")
async def get_content(request, response, content_id: str):
    content = await get_content_from_db(content_id)

    # Check if user can view this specific content
    if not request.user.has_permission(f"content.view.{content.category}"):
        raise PermissionDenied("Insufficient permissions for this category")

    return content
```

**Modify response based on permissions**:

```python
@app.get("/api/user/{user_id}")
@has_permission("users.view")  # Basic permission check
async def get_user(request, response, user_id: str):
    user_data = await get_user_data(user_id)

    # Only include sensitive fields if user has permission
    if not request.user.has_permission("users.view_sensitive"):
        user_data.pop("email", None)
        user_data.pop("last_login_ip", None)

    return user_data
```

By understanding these patterns and best practices, you can implement a robust permission system that scales with your application's needs while keeping your code maintainable and secure.

## Authentication Backends

### JWT Backend

Handles JSON Web Token authentication.

```python
from nexios.auth.backends.jwt import JWTAuthBackend
import jwt

async def load_user_from_jwt(payload: dict) -> SimpleUser:
    """Load user from JWT payload"""
    user_id = payload.get("sub")
    # Load user from database or other storage
    user_data = await db.users.find_one({"id": user_id})
    if user_data:
        return SimpleUser(username=user_data["username"])
    return None

jwt_backend = JWTAuthBackend(

    authenticate_func=load_user_from_jwt,
)
```

**Key Parameters:**

- `authenticate_func`: Function that loads user from JWT payload

### Session Backend

Handles session-based authentication.

```python
from nexios.auth.backends.session import SessionAuthBackend

async def load_user_from_session(**session_data: dict) -> SimpleUser: #enforce keyword arguments is a mapping
    """Load user from session data"""
    if "user" in session_data:
        return SimpleUser(username=session_data["user"]["username"])
    return None

session_backend = SessionAuthBackend(
    authenticate_func=load_user_from_session,
    user_key="user"  # Key in session where user data is stored
)
```

**Key Parameters:**

- `authenticate_func`: Function that loads user from session data
- `user_key`: Session key containing user data

## Protecting Route with @auth Decorator

The `@auth` decorator controls access to route handlers based on authentication status and scopes.

### Basic Usage

```python
from nexios.auth.decorators import auth

# Require any authenticated user
@app.get("/protected")
@auth(["jwt"])
async def protected_route(request: Request, response: Response):
    return {"message": f"Hello, {request.user.display_name}!"}

# Require specific scopes
@app.get("/admin")
@auth(["jwt"])
async def admin_route(request: Request, response: Response):
    return {"message": "Admin access granted"}
```

## Using Multiple Authentication Backends

Nexios supports multiple authentication backends, which are tried in order until one succeeds.

When using multiple authentication backends in Nexios, the system attempts to authenticate requests using each backend in the order they are defined. This approach provides a fallback strategy where if one backend fails to authenticate the user, the next available backend is tried.

Here's how it works:

1. **Order of Evaluation**: The backends are configured in a list, and they are evaluated in the order they appear. The system will attempt to authenticate using the first backend, and if authentication fails, it will proceed to the next backend.

2. **Successful Authentication**: As soon as a backend successfully authenticates a user, the process stops, and the user is considered authenticated. The authenticated user object is attached to the request.

3. **Fallback Mechanism**: If a backend fails to authenticate, the system automatically falls back to the next backend in the list. This continues until a backend successfully authenticates the user or all backends have been tried.

4. **Unauthenticated Request**: If none of the backends can authenticate the request, the `request.user` defaults to an `UnauthenticatedUser`. This means the request does not have a valid authenticated user, and access to secured routes will be denied.

5. **Logging and Debugging**: It's advisable to log authentication attempts, especially when multiple backends are used, to diagnose issues with the authentication flow.

The following example demonstrates setting up multiple backends:

```python
app.add_middleware(
    AuthenticationMiddleware,
    backends=[
        JWTAuthBackend(
            secret_key="jwt-secret",
            authenticate_func=load_user_from_jwt
        ),
        SessionAuthBackend(
            authenticate_func=load_user_from_session
        )
    ]
)
```

In this setup, the `JWTAuthBackend` is tried first. If it fails to authenticate the request, the `SessionAuthBackend` provides a fallback mechanism.

**Key Points:**

1. Backends are tried in the order they are specified
2. The first backend that returns a user wins
3. If no backend authenticates the user, `request.user` is an `UnauthenticatedUser`
4. The authentication method is stored in `request.scope["auth"]`

Nexios provides the `has_permission` decorator for implementing fine-grained permission checks in your application. This decorator works alongside the authentication system to ensure users have the necessary permissions to access specific routes.

### Basic Usage

```python
from nexios.auth.decorators import has_permission

# Protect a route with a single permission
@app.get("/admin/dashboard")
@has_permission("admin.access")
async def admin_dashboard(request, response):
    return {"message": "Welcome to the admin dashboard!"}

# Require multiple permissions
@app.get("/content/edit")
@has_permission(["content.edit", "content.publish"])
async def edit_content(request, response):
    return {"message": "Content editing interface"}
```

### Permission Checking with SimpleUser

The `has_permission` decorator works seamlessly with the `SimpleUser` class. Here's how to set up a user with specific permissions:

```python
from nexios.auth.base import SimpleUser

# Create a user with specific permissions
user = SimpleUser(
    username="editor",
    permissions=["content.edit", "content.view"]
)

# The decorator will check if the user has the required permissions
# before allowing access to the route
```

### Advanced Permission Scenarios

#### Public Route with Optional Authentication

```python
@app.get("/public-data")
@has_permission()  # No permissions required, but user must be authenticated
async def public_data(request, response):
    return {"message": "Public data for authenticated users"}
```

#### Complex Permission Logic

For more complex permission logic, you can combine `has_permission` with custom route handlers:

```python
@app.get("/admin/reports")
@has_permission("reports.view")  # Basic permission check
async def view_reports(request, response):
    # Additional permission logic in the handler
    if request.user.has_permission("reports.export"):
        return {"message": "Showing reports with export options"}
    return {"message": "Showing basic reports"}
```

### Error Handling

The `has_permission` decorator raises specific exceptions that you can handle globally:

- `AuthenticationFailed`: When no user is authenticated
- `PermissionDenied`: When the user is authenticated but lacks required permissions

```python
from nexios.auth.exceptions import AuthenticationFailed, PermissionDenied

@app.add_exception_handler(AuthenticationFailed)
async def handle_auth_failed(request, response, exc):
    return JSONResponse(
        status_code=401,
        content={"error": "Authentication required"}
    )

@app.add_exception_handler(PermissionDenied)
async def handle_permission_denied(request, response, exc):
    return JSONResponse(
        status_code=403,
        content={"error": "Insufficient permissions"}
    )
```

### Combining Multiple Authentication Methods

```python
# In your authentication setup
def setup_authentication(app):
    # JWT for API clients
    jwt_backend = JWTAuthBackend(
        secret_key=os.getenv("JWT_SECRET"),
        authenticate_func=load_user_from_jwt
    )

    # Session for browser-based auth
    session_backend = SessionAuthBackend(
        authenticate_func=load_user_from_session
    )

    # API key for service-to-service
    api_key_backend = APIKeyBackend(
        authenticate_func=load_user_from_api_key
    )

    # Add middleware with all backends
    app.add_middleware(
        AuthenticationMiddleware,
        backends=[jwt_backend, session_backend, api_key_backend]
    )

# In your route handlers
@app.get("/api/data")
async def get_data(request: Request):
    auth_method = request.scope.get("auth")  # "jwt", "session", or "apikey"
    return {"data": "sensitive data", "auth_method": auth_method}
```

## Custom Authentication Backends

You can create custom authentication backends by extending the `AuthenticationBackend` class. This is useful when you need to implement custom authentication logic that isn't covered by the built-in backends.

### Creating a Custom Backend

```python
from nexios.auth.base import AuthenticationBackend, BaseUser, UnauthenticatedUser

class CustomUser(BaseUser):
    def __init__(self, user_id: str, username: str, roles: list = None):
        self.user_id = user_id
        self.username = username
        self.roles = roles or []

    @property
    def is_authenticated(self) -> bool:
        return True

    @property
    def display_name(self) -> str:
        return self.username

    @property
    def identity(self) -> str:
        return self.user_id

class CustomAuthBackend(AuthenticationBackend):
    def __init__(self, authenticate_func):
        self.authenticate_func = authenticate_func

    async def authenticate(self, request: Request, response: Response) -> Any:
        # Extract credentials from the request
        auth_header = request.headers.get("X-Custom-Auth")

        if not auth_header:
            return None

        # Use the provided function to validate credentials
        user_data = await self.authenticate_func(auth_header)

        if not user_data:
            return None

        # Return a tuple of (user, auth_type)
        # The auth_type is what you'll use in @auth decorator
        return CustomUser(
            user_id=user_data["id"],
            username=user_data["username"],
            roles=user_data.get("roles", [])
        ), "custom"  # "custom" is the auth type used in @auth
```

::: Warning
the authentication method most return a tuple of (user, auth_type)
:::

### Using the Custom Backend

```python
# Define how to authenticate the custom token
async def validate_custom_token(token: str):
    # Validate the token and return user data
    if token == "valid-token":
        return {
            "id": "user123",
            "username": "custom_user",
            "roles": ["admin", "user"]
        }
    return None

# Create and configure the backend
custom_backend = CustomAuthBackend(authenticate_func=validate_custom_token)

# Add to middleware
app.add_middleware(AuthenticationMiddleware(backend=custom_backend))

# Or add with other backends
app.add_middleware(
    AuthenticationMiddleware,
    backends=[jwt_backend, session_backend, custom_backend]
)
```

## Protecting Route with @auth Decorator

The `@auth` decorator is used to protect routes by requiring specific authentication types. The authentication type corresponds to the second value returned by the backend's `authenticate` method.

### Basic Usage

```python
from nexios.auth.decorators import auth

# Require any authenticated user (any auth type)
@app.get("/protected")
@auth()
async def protected_route(request: Request):
    return {"message": f"Hello, {request.user.display_name}!"}

# Require specific authentication type (e.g., "jwt" or "custom")
@app.get("/custom-only")
@auth(["custom"])
async def custom_auth_only(request: Request):
    return {"message": "This route requires custom authentication"}

# Require multiple possible authentication types
@app.get("/api/data")
@auth(["jwt", "custom"])
async def api_data(request: Request):
    return {"data": "sensitive data"}
```

### How @auth Works with Backend Types

1. When a backend's `authenticate` method returns a user, it should also return an auth type (e.g., `"jwt"`, `"session"`, `"custom"`).
2. The `@auth` decorator checks if the request was authenticated with one of the specified auth types.
3. If no auth types are specified, any authenticated user is allowed.
4. If the auth type doesn't match, a 403 Forbidden response is returned.

### Example with Custom Backend

```python
# Custom backend returns (user, "custom") on successful authentication
class CustomAuthBackend(AuthenticationBackend):
    async def authenticate(self, request: Request, response: Response) -> Any:
        # ... authentication logic ...
        return user, "custom"  # This is the auth type

# Route that requires the custom auth type
@app.get("/custom-secure")
@auth(["custom"])
async def custom_secure_route(request: Request):
    # This route will only be accessible if authenticated via CustomAuthBackend
    return {"message": "Access granted to custom auth only"}
```

### Checking Authentication in Route Handlers

You can also check authentication status and type directly in your route handlers:

```python
@app.get("/check-auth")
async def check_auth(request: Request):
    if not request.user.is_authenticated:
        return {"status": "unauthenticated"}

    # Get the authentication type (e.g., "jwt", "session", "custom")
    auth_type = request.scope.get("auth")

    return {
        "status": "authenticated",
        "user": request.user.identity,
        "auth_type": auth_type,
        "is_admin": hasattr(request.user, "roles") and "admin" in request.user.roles
    }
```

## Complete Example: Custom API Key Authentication

Here's a complete example of implementing API key authentication:

```python
from nexios.auth.base import AuthenticationBackend, BaseUser

class APIKeyUser(BaseUser):
    def __init__(self, api_key: str, permissions: list):
        self.api_key = api_key
        self.permissions = permissions

    @property
    def is_authenticated(self) -> bool:
        return True

    @property
    def display_name(self) -> str:
        return f"API-User-{self.api_key[-6:]}"

    @property
    def identity(self) -> str:
        return self.api_key

class APIKeyBackend(AuthenticationBackend):
    def __init__(self, authenticate_func):
        self.authenticate_func = authenticate_func

    async def authenticate(self, request: Request, response: Response) -> Any:
        api_key = request.headers.get("X-API-Key")
        if not api_key:
            return None

        # Validate API key and get permissions
        permissions = await self.authenticate_func(api_key)
        if not permissions:
            return None

        return APIKeyUser(api_key, permissions), "api-key"

# Usage
async def validate_api_key(key: str):
    # In a real app, check against database
    if key == "test-key-123":
        return ["read:data", "write:data"]
    return None

api_key_backend = APIKeyBackend(authenticate_func=validate_api_key)

# Add to middleware
app.add_middleware(AuthenticationMiddleware(backend=api_key_backend))

# Protect routes with API key
@app.get("/api/data")
@auth(["api-key"])
async def get_data(request: Request, response: Response):
    return {"data": "sensitive data"}

# Or require specific permissions
@app.post("/api/data")
@auth(["api-key"])
async def post_data(request: Request, response: Response):
    if "write:data" not in request.user.permissions:
        return {"error": "Insufficient permissions"}, 403

    # Process data
    return {"status": "success"}
```

This documentation provides a comprehensive guide to implementing custom authentication backends and using the `@auth` decorator in Nexios. The examples show how to create custom user models, implement authentication logic, and protect routes based on authentication types and permissions.