To Reproduce Steps to reproduce the behavior:

• After applying recommendations from step 8 of section "6.1. Deploying RHOSO with a federated IDP" of "Configuring security services" guide, customer consistently get HTTP Not found from Keystone's public endpoint when trying to authenticate via Horizon
• We found out that "v3" suffix was missing from redirect URL
• We had to define WEBSSO_KEYSTONE_URL to explicitly point to proper keystone URL.

It looks like the problem is either in our documentation, or there is a horizon bug that doesn't allow it calculate auth_url properly, so it ends up missing "v3".

Expected behavior
Redirect works properly after following recommendations from document

Screenshots
image.png files attached to support case on 6/23/2025 and before
must-gather is attached to support case as well

Bug impact
Customer is unable to configure federation using out guide

Known workaround
To explicitly define WEBSSO_KEYSTONE_URL