Getting "error": "unsupported_grant_type" when trying to get a JWT by calling an OWIN OAuth secured Web Api via Postman
Solution 1:
The response is a bit late - but in case anyone has the issue in the future...
From the screenshot above - it seems that you are adding the url data (username, password, grant_type) to the header and not to the body element.
Clicking on the body tab, and then select "x-www-form-urlencoded" radio button, there should be a key-value list below that where you can enter the request data
Solution 2:
With Postman, select Body tab and choose the raw option and type the following:
grant_type=password&username=yourusername&password=yourpassword