By webhook, I assume you mean some form of HTTP API. You would need to look at $urlget()
Here's the info directly from the help file: /help $urlget
Note: the user:pass@address portion of the URI defines an OLD base64 authentication method (http response of: 401 unauthorized) This is NOT login/password for anything and everything, like forums or web API's etc... Logging into websites and API's you would need to form the proper query-string containing the form items and their values, for either GET method or POST method.
Once doing said login information, most sites give you a Unique ID as a cookie, which you MUST extract yourself from the $urlget().reply .. Any following calls to this website requiring this data must be formatted as valid header fields in a binvar and passed to $urlget() so it includes your extended header information (like cookies). Extra header information are NOT persistent across multiple $urlget() calls, unlike a browser.
Without further information on how you need to interact with your "Webhook" this is the best I can offer.
Downloads content from specified http/https address. Returns id number. Calls alias with id number as parameter when transfer completes.
url = http/https://user:pass@address:port/file?parameters
hgpuad = head, get, post, put, patch, or delete
fb = file or &binvar
r = resume
t = use .part file
i = ignore SSL errors
k = prevent redirects
c = cancel
target = file or &binvar
alias = called on completion
headers = &binvar
body = &binvar
If the call fails, for any reason, it returns an id of zero.
$urlget(N/id) can be used with properties: url, redirect, method, type, target, alias, id, state, size, resume, rcvd, time, reply