Unable to proxy websockets?

I'm trying to use Phoenix LiveView over tunnelto. Everything works just fine without proxy or when using ngrok.
With tunnelto I get:

```
[info] Sent 200 in 2ms
[info] CONNECTED TO Phoenix.LiveView.Socket in 25µs
Transport: :websocket
Serializer: Phoenix.Socket.V2.JSONSerializer
Parameters: %{...}
[debug] LiveView session was misconfigured or the user token is outdated.

1) Ensure your session configuration in your endpoint is in a module attribute:

@session_options [
...
]

2) Change the `plug Plug.Session` to use said attribute:

plug Plug.Session, @session_options

3) Also pass the `@session_options` to your LiveView socket:

socket "/live", Phoenix.LiveView.Socket,
websocket: [connect_info: [session: @session_options]]

4) Ensure the `protect_from_forgery` plug is in your router pipeline:

plug :protect_from_forgery

5) Define the CSRF meta tag inside the `` tag in your layout:

<%= csrf_meta_tag() %>

6) Pass it forward in your app.js:

let csrfToken = document.querySelector("meta[name='csrf-token']").getAttribute("content");
let liveSocket = new LiveSocket("/live", Socket, {params: {_csrf_token: csrfToken}});
```

This happens in all browsers.
Standard HTTP requests are proxies just fine.
tunnelto version is 0.1.18.