Authentication requires sending form data.
In cURL, the application/x-www-form-urlencoded or multipart/form-data header must be specified.
The image below shows token generation using the Postman application.
Note: If you have previously used standard authentication in Postman (on the Auth tab), you must clear those credentials.
The response will contain the generated token:
{"authSessionId": "43cced75ff51351aaf5a6492b618d2e8749f9aa1e489272e80c9135453347e69", "success":true}