Authentication middleware IndexError on instance method 

### Checklist

- [x] The bug is reproducible against the latest release and/or `master`.
- [x] There are no similar issues or pull requests to fix it yet.

### Describe the bug

We are using a wrapper around FastAPI which makes it possible to create routes on classes with endpoints on the methods. This makes it easier to manage dependency injection among others.

When we add authentication middleware to our application, the authenticated endpoints fail due to `IndexError: tuple index out of range`. 

This error occurs at `authentication.py:60` 
```python
request = kwargs.get("request", args[idx] if args else None)
```

We use the following definitions:

```python
@router.endpoint("/")
class Main:   
    @router.get("/")
    async def hello(self):
        return {"greeting": "Hello unknown!"}
 
    @requires("admin")
    @router.get("/authorized")
    async def authorized(self, request: Request):
        return {"greeting": f"Hi {request.user.display_name()}, you're authorized, so welcome!"}
```

We have created the class decorator for endpoint ourselves.

I looked in the debugger and both `args` and `kwargs` contain values. `args` contains `self` for the instance method and `kwargs` contains `request`. This causes the `if args` check to pass, which means `args[idx]` will cause an IndexError. This can be fixed by adding an additional check: 
```python
request = kwargs.get("request", args[idx] if args and idx < len(args) else None)
```

### To reproduce

It is not easily possible to create a reproduction example due to our custom wrapper around FastAPI. Implementing this fix does fix the problem for us though. 

To reproduce:

<details>

```python
import typing

from fastapi import APIRouter, FastAPI
from starlette.authentication import AuthCredentials, AuthenticationBackend, requires, SimpleUser, BaseUser
from starlette.requests import HTTPConnection, Request
from starlette.middleware.authentication import AuthenticationMiddleware


class AuthBackend(AuthenticationBackend):

    async def authenticate(self, conn: HTTPConnection) -> typing.Optional[typing.Tuple["AuthCredentials", "BaseUser"]]:
        return AuthCredentials(["TheScope"]), SimpleUser("TheUser)")


app = FastAPI()
app.add_middleware(AuthenticationMiddleware, backend=AuthBackend())


class Main:
    @requires("TheScope")
    def some_route(self, request: Request):
        return {'hello': 'world'}


main = Main()
router = APIRouter()
router.add_api_route('/', main.some_route, methods=['GET'])

app.include_router(router)

# Finally, call GET '/'
```

</details>

### Expected behavior

When a request is made to an authentication endpoint the request either returns "forbidden" when the authentication is not valid or returns the required response.

### Actual behavior
The authentication wrapper `requires` fails when the request is made. This happens due to an `IndexError` when idx >= len(args).

### Debugging material


Traceback:
<details>

```
ERROR:uvicorn.error:Exception in ASGI application
Traceback (most recent call last):
  File "C:\Users\<path-to-virtual-env>\lib\site-packages\uvicorn\protocols\http\h11_impl.py", line 394, in run_asgi
    result = await app(self.scope, self.receive, self.send)
  File "C:\Users\<path-to-virtual-env>\lib\site-packages\uvicorn\middleware\proxy_headers.py", line 45, in __call__
    return await self.app(scope, receive, send)
  File "C:\Users\<path-to-virtual-env>\lib\site-packages\allseas_api\api.py", line 63, in __call__
    await self._fast_api.__call__(scope, receive, send)
  File "C:\Users\<path-to-virtual-env>\lib\site-packages\fastapi\applications.py", line 179, in __call__
    await super().__call__(scope, receive, send)
  File "C:\Users\<path-to-virtual-env>\lib\site-packages\starlette\applications.py", line 111, in __call__
    await self.middleware_stack(scope, receive, send)
  File "C:\Users\<path-to-virtual-env>\lib\site-packages\starlette\middleware\errors.py", line 181, in __call__
    raise exc from None
  File "C:\Users\<path-to-virtual-env>\lib\site-packages\starlette\middleware\errors.py", line 159, in __call__
    await self.app(scope, receive, _send)
  File "C:\Users\<path-to-virtual-env>\lib\site-packages\starlette\middleware\gzip.py", line 18, in __call__
    await responder(scope, receive, send)
  File "C:\Users\<path-to-virtual-env>\lib\site-packages\starlette\middleware\gzip.py", line 35, in __call__
    await self.app(scope, receive, self.send_with_gzip)
  File "C:\Users\<path-to-virtual-env>\lib\site-packages\starlette\middleware\authentication.py", line 48, in __call__
    await self.app(scope, receive, send)
  File "C:\Users\<path-to-virtual-env>\lib\site-packages\starlette\exceptions.py", line 82, in __call__
    raise exc from None
  File "C:\Users\<path-to-virtual-env>\lib\site-packages\starlette\exceptions.py", line 71, in __call__
    await self.app(scope, receive, sender)
  File "C:\Users\<path-to-virtual-env>\lib\site-packages\starlette\routing.py", line 566, in __call__
    await route.handle(scope, receive, send)
  File "C:\Users\<path-to-virtual-env>\lib\site-packages\starlette\routing.py", line 227, in handle
    await self.app(scope, receive, send)
  File "C:\Users\<path-to-virtual-env>\lib\site-packages\starlette\routing.py", line 41, in app
    response = await func(request)
  File "C:\Users\<path-to-virtual-env>\lib\site-packages\fastapi\routing.py", line 182, in app
    raw_response = await run_endpoint_function(
  File "C:\Users\<path-to-virtual-env>\lib\site-packages\fastapi\routing.py", line 133, in run_endpoint_function
    return await dependant.call(**values)
  File "C:\Users\<path-to-virtual-env>\lib\site-packages\starlette\authentication.py", line 60, in async_wrapper
    request = kwargs.get("request", args[idx] if args else None)
IndexError: tuple index out of range

```
</details>

### Environment

- OS: Windows
- Python version: 3.9.7
- Starlette version: 0.17.0

### Additional context

We need to add bearer token authentication to our endpoints. Our endpoints are methods on class instances.

Navigation Menu

Uh oh!

Authentication middleware IndexError on instance method #1334

Checklist

Describe the bug

To reproduce

Expected behavior

Actual behavior

Debugging material

Environment

Additional context

Metadata

Assignees

Labels

Projects

Milestone

Relationships

Development

Uh oh!

Authentication middleware IndexError on instance method #1334

Description

Checklist

Describe the bug

To reproduce

Expected behavior

Actual behavior

Debugging material

Environment

Additional context

Activity

Metadata

Metadata

Assignees

Labels

Projects

Milestone

Relationships

Development

Issue actions