Which Auth header is used in contacting OpenID UserInfo endpoint

In the documentation of the UserInfo endpoint usage here

It does not say which Auth header mechanism Grafana will use to contact the UserInfo endpoint.
The OpenID spec suggests that the Auth header for userinfo is a bearer token.

So do the client_id and client_secret in the config get used somehow to generate a bearer token?
Or is it some other mechanism?

We are creating our own OpenID implementation and just need to understand which OpenID endpoints Grafana expects.

Grafana does not support / use OpenID but OAuth.

It will use the OAuth token when accessing the userinfo endpoint