Azure Application Gateway Redirection from empty hostname - azure

Question

I have created an Application Gateway that needs to fulfill the working of my previous Resource (F5).
As a listener I use a hostname: hostname.stackoverflow.com that listens on 443
As a Http Setting I am using a specific port being 4443
As a BackEnd pool I use the URL/FQDN of my dev VM.
This totally works If i create a VM in the VNET and add "hostname.stackoverflow.com" to the hosts file with the ip of the application gateway.
Now I want to get a little further and add paths to my Application Gateway.
The goal is that if I use "hostname.stackoverflow.com" I need to redirect this to "Hostname.stackoverflow.com/login.aspx?guestlogin".
As far I have tried the following.
Add the "/login.aspx?guestLogin" to the HTTPS settings like this.
When I try this inside my VM. The URL changes but the path that I added there was not added in the right way, This is what I got:
So That made me think override backend path is maybe not the right way to do this.
Wanted To create a Redirection Rule That will redirect my "hostname.stackoverflow.com" to the "hostname.stackoverflow.com/login.aspx?guestLogin" But in the settings of the Application Gateway I need to provide a source path (meaning: I can not redirect from an empty hostname to a new url I think)
I am very new to Azure and even more new to the Application Gateway. Is there something that I did wrong. Is there a better way to do this ?
The iRule that I need to get in Application Gateway is as followed.
if { [string tolower [HTTP::host]] equals "hostname.stackoverflow.com" } {
if {[HTTP::path] eq "/"} {
HTTP::redirect "login.aspx?guestLogin"
}
elseif {[string tolower [HTTP::uri]] starts_with "/login.aspx?id="} {
set tail [string range [HTTP::uri] 12 end]
HTTP::redirect "login.aspx?guestLogin&$tail"
}
pool default.pool
}