OAuth - custom redirect_url for proxys

[ghost]

Is your feature request related to a problem? Please describe.
When connecting a proxy inbetween the user and the application this occurrs. As the app has a internal dns entry and a public dns entries the proxy handels the forwarding. The used proxy is Application Proxy by Microsoft.
https://learn.microsoft.com/en-us/entra/identity/app-proxy/application-proxy

This proxy puts a "layer on top" of Thruk and provides a secure way to access apps via the microsoft datacenter and OAuth2 preconfigured by microsoft. After this layer the OAuth2 via Thruk can be configured. However this needs the external dns entry, but thruk only takes the loginpage url which is the internal proxy url. Therefore we need to modify thruk to include the option to modify this entry to custom.
The error is this:

Something like this is the workflow of application proxy.

User -> Public DNS Entry -> OAuth via Microsoft (DDOS etc.) -> Login via Microsoft -> App proxy internal url -> Thruk -> Login via OAuth2 by Thruk -> UI

Describe the solution you'd like
Add to OAuth.pm & Documentation the following.
Adds a read from the config file to read the parameter redirect_url this redirect url can be configured inside the application with microsoft.

Line 60 to 67

        my $res = $ua->post($auth->{'token_url'}, {
                                    client_id       => $auth->{'client_id'},
                                    client_secret   => $auth->{'client_secret'},
                                    code            => $code,
                                    redirect_uri    => $auth->{'redirect_url'},
                                    state           => $state,
                                    grant_type      => 'authorization_code',
        });

Line 150 to 156

    my $oauth_login_url = Thruk::Utils::Filter::uri_with($c, {
                                    client_id       => $auth->{'client_id'},
                                    scope           => $auth->{'scopes'},
                                    state           => $state,
                                    response_type   => 'code',
                                    redirect_uri    => $auth->{'redirect_url'},
                            }, 1, $auth->{'auth_url'}, 1);

Describe alternatives you've considered
There are no alternatives to make oauth2 work with azure application proxy and the native thruk oauth plugin.

Additional context
See above.

[ghost]

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