How to add authorization HTTP header?

Your MCP proxy is awesome, thanks for sharing it! Now, I'm trying to do something like this:

```
  "mcpServers": {
    "example": {
      "command": "npx",
      "args": [
        "mcp-server-and-gw", 
        "https://example.com/",
        "AUTH_TOKEN=foo"
      ]
    }
  }
```

Here, `AUTH_TOKEN` is the HTTP header to be sent to the `example.com` server with every HTTP request. Is it possible?