Visibility of Single-Sign-On button depends on referrer

Problem/Motivation

The visibility of the single sign on button on the Drupal login page (with CiviCRM plugin) depends on what the browser reports as the referrer.

Steps to reproduce

1. Take Drupal basis container (here: drupal:9.5.5-php8.1-apache-bullseye)
2. Install CiviCRM plugin (here v5.59.0)
3. Install Drupal LDAP plugin (here v4.3) and configure it against an LDAP directory
4. Install Drupal Keycloak plugin (here v1.7) and configure it against Keycloak instance that syncs with LDAP directory

You can see the behaviour here in our test instance (in German language):

1. Go directly from here to https://civicrm.apps.dev.iog-cloud.org/user/login
2. No Keycloak button shown

1. First, go to https://civicrm.apps.dev.iog-cloud.org/civicrm
2. Then, go to https://civicrm.apps.dev.iog-cloud.org/user/login
3. Keycloak button is shown

Proposed resolution

Visibility of SSO button should not depend on referrer.

Remaining tasks

User interface changes

API changes

Data model changes