Verifying OIDC app client credentials

I have a web service that stores the Issuer URL, client ID and secret (or private key) to allow users to authenticate with Okta via OIDC. I want my service admins to be able to verify that the OIDC config stored in the service is correct.

For Azure EntraID I’m able to request the client token using the Client Credentials flow, and thus fully verify my service connection settings.

I was able to do the same thing with Okta using the Authorization Server, but my client doesn’t have this extra product (Okta API Access Management) and doesn’t intend to buy it, because they don’t need it. Is there any way that it can be done without it?

The following topic proposes an alternative, but I don’t get it. Is it described anywhere in detail?

The referenced article still mentions the Authorization Server, so it seems it doesn’t solve the issue:

Also the proposed solution would require a redirect in the browser, but that’s not acceptable. I want to verify the service credentials, not user credentials.

Creating a Service app also wouldn’t make any sense, as it would use different credentials.

So, how can I verify my OIDC setup server-side?