Reply URL for AAD Sign-in button does not work

> [!IMPORTANT]
> **PLEASE DO NOT CREATE ISSUES RELATED TO MANAGED DEVELOPER PORTAL IN THIS REPOSITORY**. Issues related to "Managed developer portal" will be closed automatically. Managed developer portal issues should be created directly in Azure Support + Troubleshooting in Azure portal. Contact Azure support (or) submit a post [on Stack Overflow](http://aka.ms/apimso). Feature requests can be raised [on the Azure Feedback Forum](https://aka.ms/apimwish).

Every self-hosted developer bug report should have precise description and reproduction steps; console traces (or) source code references are appreciated.

## Bug description

I am using an AAD sign in button in my portal. I have been fighting with it forever to try to get it to redirect to the SAME PAGE that the button is on, but no matter what I do, it redirects to the home page. So, my button is on /apiSandbox, and when the user signs in, it kicks them to the home page at /. I have tried putting in a custom reply URL of /apiSandbox on the button itself, I have tried with a blank URL, and it does not work.

## Reproduction steps

1. Create AAD sign in button on non-home page.
2. Configure to use no reply URL (functionality is supposed to use current page URL)
3. Publish
4. Sign in, button will kick user to home page
5. Try the same thing but manually put the reply URL as the URL of the page on which the button exists

## Expected behavior

Redirect to the page on which the button exists instead of to the home page.

## Is self-hosted portal?

Yes
> [!WARNING]
> "Managed developer portal issues" will be closed automatically. See above for more details.

## Release tag or commit SHA (if using self-hosted version)

20240812141213

## API Management service name

ams-dev-scus-core

## Environment

- Operating system: Windows
- Browser: All browsers tested - Chrome, Edge, Firefox
- Version: All

## Additional context

Add any other context about the problem here, including screenshots.

Start by reproducing the AAD sign-in button flow on a published self-hosted portal page such as /apiSandbox, testing both an empty and an explicit reply URL. Compare the resulting redirect with the expected current-page URL and check the portal's sign-in button configuration and authentication entry points. Done means sign-in returns to the page containing the button in both configurations.

Written by the indexing model from the issue text.