add ability to add custom request headers

I'm looking for a way to customize the DashRenderer request HTTP headers, mainly for authentication purposes. There's a thread on the community forum that wasn't resolved, but otherwise I don't see any discussion, either on GitHub or on the forum. I was wondering, has there been any progress on this? And if not, would you be willing to accept help and/or help me out creating a PR for this?

It looks to me a reasonably straightforward solution would be to modify the handleServerside callback to look something like this:

function handleServerside(
    hooks: any,
    config: any,
    payload: any
): Promise<any> {
    let rawRequest = mergeDeepRight(config.fetch, {
        method: 'POST',
        headers: getCSRFHeader() as any
    });

    if (hooks.request_pre !== null) {
        hooks.request_pre(payload, rawRequest);
    }

    rawRequest.body = JSON.stringify(payload);
    return fetch(
        `${urlBase(config)}_dash-update-component`,
        rawRequest
    ).then(...)
}

and then to modify the request_pre hook to accept an additional parameter.

Alternatives I can think of:

• Expose only the headers as an additional parameter to the request_pre hook.
• Expose the config object to a new (pre-load) hook

What are your thoughts on this?

Start at the DashRenderer handleServerside callback and the existing request_pre hook described in the issue. Compare the proposed ways to expose request headers or config, then define a completed design in which callers can customize headers for authenticated requests and the relevant request behavior is covered.