Problem using /oauth/token REST API


I am trying to use the “/oauth/token” REST API to verify user’s password.
This API always return HTTP 401, even when the user&password provided are valid.
Is there a special configuration I need to enable for this API?

Here is the HTTP details:

POST /oauth/token HTTP/1.1
Content-Length: 160
Content-Type: application/json
“client_id”: “client_id”,
“grant_type”: “password”,
“password”: “123456”,
“scope”: “scope123”,
“username”: “
** Response **:
HTTP/1.1 401
status: 401
date: Sun, 21 Jan 2018 17:11:07 GMT
content-type: application/json
x-auth0-requestid: 23424234
x-ratelimit-limit: 1000000
x-ratelimit-remaining: 999999
x-ratelimit-reset: 1516554668
www-authenticate: Basic realm=“Users”
cache-control: private, no-store, no-cache, must-revalidate, post-check=0, pre-check=0

As it has been more than a few months since this topic was opened, and there has been no reply or further information provided as to the existence of the issue, we are closing this topic. Please don’t hesitate to create a new topic if this issue is still present, we would be happy to work with you to help find a resolution.