Configuring a custom Relative URL on the Self-Service UI tab in System Preferences seems to break social registration. Note: there is no reverse proxy involved in this setup.
Steps to reproduce:
Then login using a social provider with an account that doesn't already exist in IDM:
Observe the error:
The developer tools show the issue:
The UI is trying to make a call to a non-existing endpoint at:
The URL contains the custom Self-Service URL configured (/user) and also considered the well-known URL (/openidm).
As a result, the user is not created and not authenticated.