> ## Documentation Index
> Fetch the complete documentation index at: https://docs.chainlit.io/llms.txt
> Use this file to discover all available pages before exploring further.

# Header

Header auth is a simple way to authenticate users using a header. It is typically used to delegate authentication to a reverse proxy.

The `header_auth_callback` function is called with the headers of the request. It should return a `User` object if the user is authenticated, or `None` if the user is not authenticated.
The callback function (defined by the user) is responsible for managing the authentication logic.

## Example

```python theme={null}
from typing import Optional

import chainlit as cl


@cl.header_auth_callback
def header_auth_callback(headers: Dict) -> Optional[cl.User]:
  # Verify the signature of a token in the header (ex: jwt token)
  # or check that the value is matching a row from your database
  if headers.get("test-header") == "test-value":
    return cl.User(identifier="admin", metadata={"role": "admin", "provider": "header"})
  else:
    return None
```

Using this code, you will not be able to access the app unless the header `test-header` is set to `test-value` when sending any request to the app.