Issue
A third party integration trying to retrieve OAuth token from the instance with a GET call fails with "access_denied"
Cause
To retrieve the token from the instance you can only make a POST call and not a GET call since you are passing data to the call like clientID, Client secret, grant type etc.
Resolution
Make a POST call instead of GET
Related Links
Sending sensitive information over URI query parameters may lead to sensitive information disclosure by clients, the server, or any host between the requests.
