The X-Callback header is a proposal for a common way to describe HTTP callbacks, primarily in the case of registering them.
Great proposal from my former Twilio colleague Jeff Lindsay for instructing a server to respond to an HTTP request via a callback instead of a synchronous response.
A couple of tweaks I would suggest:
- Rename the header name to
Callback-Location(or something). X- prefixed headers are being discouraged these days.
- Use a 2xx class response code to indicate that the request was received and the callback registered. The current definitions of 200-206 don’t fit well enough for my liking.
Jeff is working on advancing the state of Webhooks into something more standard-like, so his blog is definitely one you’ll want to keep an eye on.