Automatic redirection issue when portal self hosted with azure app service and azure waff!

Instead of hosting the static files using a blob storage we have hosted the static files using a app service. The app service is using nginx server. And a waff is configured with custom domain.

The Problem

When you a host a website using azure app service it gives a default url with which we can visit the website, lets say : https://appname.azurewebsites.net.
We have set up a waff that points the app to a custom domain, lets say - https://example.com.
When I visit the domain https://example.com, it takes me to the index.html with no problem. But when visiting any other pages like signin, apis, products, etc pages the domain before the path automatically changes to the app service url i.e. https://appname.azurewebsites.net/signin or https://appname.azurewebsites.net/apis.
Which should be https://example.com/signin or https://example.com/apis respectively.
And when I try to forcefully visit any other page with custom domain name the url automatically changes to app service url.

We have made only CSS changes in the developer portal code. No typescript code was changed.
Need help, any responses will be highly appreciated. Thanks!!