User pool third-party OIDC - token request

I am setting up a third-party OIDC provider with my Cognito user pool that is only enabled for using the Authorization code grant. I've noticed that when AWS makes the request to my token endpoint, it includes the Client ID and Client Secret as fields in the POST request body, rather than in the Authorization header. Is there any configuration that can change this behavior to the more standard use of the Authorization header?