[Feature Request] Configurable pre-login notice / consent page in UAA

Summary

We have a requirement to show a pre-login notice on the UAA login flow, before the user can enter credentials or proceed to authenticate.

Today, UAA allows some limited customization of the login UI via branding options (banner text/logo, footer legal text, footer links such as Support / Terms of Service, and basic theming). However, there is no built-in way to show a blocking pre-login notice or consent message that must be acknowledged before login can proceed.

We would like UAA to support a configurable pre-login notice / consent step that can be used for things like:

• Terms of Service
• Acceptable Use Policy
• End-User License Agreement
• Service Terms & Conditions
• Privacy Notice
• Data Processing Notice
• Data Collection Consent
• Cookie & Tracking Disclosure (if applicable)
• Security Warning
• Authorized Use Notice
• Confidential Systems Notice
• Important Notice
• Before You Continue
• Usage Guidelines
• Organization Policy

This feature should be opt-in and preserve current login behavior by default.

Start by tracing the UAA login flow and reviewing the existing branding configuration described in the issue. The work is done when an opt-in pre-login notice or consent step blocks authentication until acknowledged, while the default login behavior remains unchanged.