Add Multi-domain routing support similar to Next.JS SDK so that default language is set for specific hostname

[ivanbuzyka]

What would you add to the SDK?

Curently it is possible to set default language globally for the entire Head Application, see in Program.cs:

const string defaultLanguage = "en";
const string germanLanguage = "de-DE";
app.UseRequestLocalization(options =>
    {
        // If you add languages in Sitecore which this site / Rendering Host should support, add them here.
        List<CultureInfo> supportedCultures = [new CultureInfo(defaultLanguage), new CultureInfo(germanLanguage)];
        options.DefaultRequestCulture = new RequestCulture(defaultLanguage, defaultLanguage);
        options.SupportedCultures = supportedCultures;
        options.SupportedUICultures = supportedCultures;
        options.UseSitecoreRequestLocalization();
    });

Next.JS SDK has the way to configure default language per website domain/hostname, see this recipe for more information: https://developers.sitecore.com/learn/accelerate/xm-cloud/implementation/information-architecture/localization#multi-domain-routing-with-localization

This is useful functionality that allows more advanced multi-site configuration.
The scenarios like following are possible in Next.js but currently they are not possible for ASP.NET Core SDK:

1. ASP.NET Core SDK app should serve 2 websites: www.test.nl and www.anothertest.de
2. When visited, www.test.nl should set localization to NL so that content from layout service is delivered in NL language. No redirection or /nl-NL prefix should be used in the URL
3. When visited www.anothertest.de should set localization to de-DE and the content should be delivered o de-DE version. Again, no /de-DE language prefix should be used in the URL.

Code of Conduct

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[pbering]

You can pretty easy do it by adding your own implementation of an Microsoft.AspNetCore.Localization.RequestCultureProvider add it right after options.UseSitecoreRequestLocalization(); like so:

options.RequestCultureProviders.Add(new HostnameRequestCultureProvider());

Simple implementation:

public class HostnameRequestCultureProvider: RequestCultureProvider
{
    public override Task<ProviderCultureResult?> DetermineProviderCultureResult(HttpContext httpContext)
    {
        ArgumentNullException.ThrowIfNull(httpContext);

        var culture = httpContext.Request.Host.Host switch
        {
            "www.test.nl" => "nl-NL",
            "www.anothertest.de" => "de-DE",
            _ => "en",
        };

        return Task.FromResult<ProviderCultureResult?>(new ProviderCultureResult(culture, culture));
    }
}

The SDK uses this value when doing layout requests: https://github.com/Sitecore/ASP.NET-Core-SDK/blob/main/src/Sitecore.AspNetCore.SDK.RenderingEngine/Configuration/RenderingEngineOptions.cs#L23