Supporting OKTA OAuth 2.0 Client Credentials Grant Flow

Error description

I try to get an token from OKTA via swagger. I can only use the client_credentials flow. I am able to get a valid token when I do the request manually with curl.

When I am using swagger I get the following error:

auth errorError: Unauthorized, error: invalid_client, description: Browser requests to the token endpoint must use Proof Key for Code Exchange.

According to OKTA on https://support.okta.com/help/s/article/Browser-requests-to-the-token-endpoint-must-use-Proof-Key-for-Code-Exchange?language=en_US it is not allowed to send the origin header when a token is requested. Unfortunately the origin header is sent.

Do you have any workarounds?

Configuration

Swagger/OpenAPI definition: 3.0
Swashbuckle.AspNetCore 5.2.3

I also played with UsePkceWithAuthorizationCodeGrant and UseBasicAuthenticationWithAccessCodeGrant but that did not work.

Start by reproducing the Swagger UI OAuth 2.0 client_credentials request against an OKTA token endpoint, comparing the browser request with the working curl request. Inspect how Swagger UI sends the token request and determine whether the Origin header can be omitted or the flow otherwise supported; done means a documented or verified workaround for this configuration.