Hi Saurabh - (Jagan thanks for bringing this to our attention)
This is possible if you disable Standard mode - documentation here:
It looks like you were attempting to use the Web File data connection and then populate the URL field with the URL you put in the original post. This WILL NOT WORK - with the default data connection mode. If you disable standard mode, YOU CAN USE the variables - but you need to put the connection information in the script - JUST LIKE YOU WOULD when using QlikView.
Just a note worth mentioning in relation to someone facing similar issues.
Sometimes the client may have different groups accessing the same app and then need to refresh from separate data sources. We would typically use variables in similar situation. You can explore applying the new rule based security to data connections via the server to solve the issue.