Unable to forward all the request headers to external auth server using SecurityPolicy CRD

## Issue: Unable to Forward All Request Headers to External Auth Server in SecurityPolicy

### Environment
- **Envoy Gateway Version:** v1.6.1
- **Installation Method:** Following the [official external auth documentation](https://gateway.envoyproxy.io/docs/tasks/security/ext-auth/)

### Problem Description

I'm implementing custom authentication using an external auth server with Envoy Gateway's `SecurityPolicy` resource. By default, only the following headers are forwarded to the auth server:

- `host`
- `content-length`
- `x-envoy-internal`
- `x-envoy-expected-rq-timeout-ms`

### Expected Behavior

I need to forward **all incoming request headers** to the external auth server for authentication purposes.

### Current Configuration

```yaml
apiVersion: gateway.envoyproxy.io/v1alpha1
kind: SecurityPolicy
metadata:
name: pty-custom-auth
namespace: test-gateway
spec:
targetRefs:
- group: gateway.networking.k8s.io
kind: HTTPRoute
name: auth-server-route
extAuth:
headersToExtAuth:
- "*"
http:
path: "/auth"
backendRefs:
- name: auth-server-service
namespace: test-gateway
port: 80
headersToBackend: ["temp-roles", "temp-username"]
```

### Attempted Solutions

I've tried multiple variations in the `headersToExtAuth` field, but none have successfully forwarded all headers:

1. `headersToExtAuth: ["*"]` - Only forwards the 4 default headers
2. `headersToExtAuth: ["."]` - Same result
3. `headersToExtAuth: [".*"]` - Same result
4. `headersToExtAuth: [""]` - Same result

### Questions

1. Is forwarding all incoming headers to the external auth server currently supported in Envoy Gateway's `SecurityPolicy` API?
2. If yes, what is the correct configuration to achieve this?
3. If not, are there any workarounds or plans to support this functionality?

Any guidance would be greatly appreciated!