Calling /oauth/token Returns Grant Type 'client_credentials' Not Allowed for the Client

Knowledge Articles
1

Overview

This article explains why it is not possible to enable the Client Credential Grant Type on an application that was changed from a Native application type to a Machine-to-Machine application type. The option is greyed out in the UI, and attempting to retrieve an access token using an API call results in the following error:

“error”:“unauthorized_client”, “error_description”:“Grant type ‘client_credentials’ not allowed for the client.”

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{
 "error":"unauthorized_client",
 "error_description":"Grant type 'client_credentials' not allowed for the client.",
 "error_uri":"https://auth0.com/docs/clients/client-grant-types"
}

Applies To

  • Client Credentials Grant

Cause

Client Secret (Post) is not turned on due to the change in the Application Type.

If the Application Type is changed after creating an application, not all settings will automatically change to match the new Application Type. The settings need to be adjusted manually.

Solution

Go to Dashboard > Applications > Applications and choose the newly created application. Select the Credentials tab and select Client Secret (Post) and select Save.

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Creating a new application with an Application Type Machine to Machine is strongly recommended.