I was presented with three different URLs (stages): 1. Authorization Endpoint, 2. Token Endpoint and 3. User Info Endpoint. I am not sure which one to use. Instinctively I went for 1. but since I am getting an fatal for all of them I am unsure which one to select.
Topic on Extension talk:OpenID Connect
It is actually none of those. It is the URL that is used for auto-discovery. When you append '/.well-known/openid-configuration' to that URL, it will point to a location that will return JSON containing those other URLs. See https://openid.net/specs/openid-connect-discovery-1_0.html#ProviderConfigurationRequest.
For example, you use https://accounts.google.com for Google, which is used to find https://accounts.google.com/.well-known/openid-configuration, which contains the other URLs.
Thank you for your reply and insight. From this is was able to figure out the correct URL. Admittedly, if I had read the existing docu more thoroughly I should have figured it out myself. Still I have adapted the existing docu to make this even more clear.