Question,

I'd like to pass a header together with the webhook.

More specifically, when calling your own Sell API's to e.g. create a Lead, the API requesters the following header to be present: 

content-type: application/json

Similar, to connect to a website/api behind Cloudflare Access we need to add

CF-Access-Client-Id: <Client ID>
CF-Access-Client-Secret: <Client Secret>

Is there a way to add these to the Webhooks without resorting to a middleware that processes the requests and adds a webhook?

See also this blog post:

https://tripelhop.dev/blog/shortcomings-of-zendesk-webhooks