SAML: Authentication issue instant is too old or in the future

On SAML-based access to Console and Enduser, it might happen that the error "Session expired: please log in again" is displayed, after successful round-trip to the configured IdP.

After investigation, the reason seems to be that some IdP is re-using information that the user has authenticated earlier (reporting that via the authnInstant in the SAML response).
By default, pac4j (the underlying library on which SAML-based access to Console and Enduser is implemented) will prevent users from login if the authentication instant is older than 1 hour (3600 seconds).