Which Auth header is used in contacting OpenID UserInfo endpoint

In the documentation of the UserInfo endpoint usage here
http://docs.grafana.org/installation/configuration/#auth-generic-oauth

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