Ticket is closed. Didn’t recognize it. Today I looked inside the log file for another reason and remembered that there was an issue. It changed a little bit. Instead of 401 it is now 403.
So that would suggest that from this provider point of view, the access token is not enough to be allowed to access the file behind the provided URL.
That being said, when given how the URL looks, it feels like the problem is not so much that the way the OIDC picture is downloaded is wrong and more the fact that the provider just indicated a URL that does not make any sense. Problem is that I have no idea how to identify that this URL should not be followed (in theory if the user does not have a picture the provider should just not indicate one).