Ah, I see, sorry for the misunderstanding. I've used Workato's "webhook" trigger for that same purpose... it provides an API endpoint that can be called without authentication to serve as a notification endpoint of a change being made elsewhere. The webhook wizard is pretty good, where it gives you the endpoint and then listens. Meanwhile you go to the other system and generate the call, and Workato "detects" it and generates the input schema for you.
The part I'm not familiar with is generating an HTML response. Mine doesn't give a response beyond the 200 Ok, and their doc looks like it's not meant to give much more.
And the API Platform, if you have that module, doesn't have an authentication-less option. But it can just use an Auth Token in plain text so you can "approximate" no authentication? ๐ My responses for those have always been JSON. It looks like the Content Type options are JSON and Text/Xml, so I'm not sure HTML would be supported. I'd ask Support to be sure on that one.
Sorry I couldn't be more help.
