
This is the simplest request that will create this workflow rule:
Some notes:
1. the Url should be ../metadata/object/Workflow
2. You get a return value from this call. I suggest to make sure to delete the created Workflow using the DELETE method since it will leave hanging workflows in your account and there's a limit to how many of these you can create.
{
"forType": "WorkItem",
"name": "My Rule",
"triggerType": "CreateOrEdit",
"criteria": "False",
"action": {
"Url": "http://www.example.org/WebHook",
"method": "POST"
}
}