How to get the current domain name in Startup.cs - asp.net-core

Question

I have a domain that has multiple sites underneath it.
In my Startup.cs I have the following code
public void ConfigureServices(IServiceCollection services)
{
services.AddIdentity<ApplicationUser, ApplicationRole>(options =>
{
options.Cookies.ApplicationCookie.CookieName = "MyAppName";
options.Cookies.ApplicationCookie.ExpireTimeSpanTimeSpan.FromMinutes(300);
})
.AddEntityFrameworkStores<MyDbContext, Guid>()
.AddDefaultTokenProviders();
On the production machine all my sites are in a subfolder under the same site in IIS so I don't want to use the default domain as the cookie name otherwise different sites cookies will have the same name
What I want is to get the current domain e..g mydomain.com and then append it to an explicit cookiename per site that I specify in Startup.cs e.g.
var domain = "get the server domain here somehow e.g. domain.com";
...
options.Cookies.ApplicationCookie.CookieName = "MyAppName." + domain;
How do I do this?
The reason I ask:
I can see in Chrome developer tools the cookies fall under separate domain names of the site I am accessing. However I sometimes somehow still get the situation of when I log into the same site on two different servers, that I can't log into one and it doesn't log any error. The only solution is to use another browser so I can only assume by the symptoms can only be to do with the cookie.
So my question is really just a personal preference question as in my environment I would prefer to append the domain name to the cookie name although the cookie can only belong to a specific domain.

Answer 1

First of all, i would store domain name in configuration. So it would enable me to change it for current environment.
options.Cookies.ApplicationCookie.CookieName = Configuration["DomainName"];
If you don't like this way you can override cookie option on signin event like this(i am not sure below ways are good):
Events = new CookieAuthenticationEvents()
{
OnSigningIn = async (context) =>
{
context.Options.CookieName = "MyAppName." + context.HttpContext.Request.Host.Value.ToString();
}
}
Or catch first request in configure and override options
bool firstRequest = true;
app.Use(async (context, next) =>
{
if(firstRequest)
{
options.CookieName = "MyAppName." + context.HttpContext.Request.Host.Value.ToString();
firstRequest = false;
}
await next();
});
Also see similar question How to get base url without accessing a request

Answer 2

I found this other way. also I have a blog to documented that.
public class Startup
{
public IConfiguration Configuration { get; }
private WebDomainHelper DomainHelper;
public Startup(IConfiguration configuration)
{
Configuration = configuration;
}
// This method gets called by the runtime. Use this method to add services to the container.
public void ConfigureServices(IServiceCollection services)
{
services.AddHttpContextAccessor();
services.AddScoped(sp => new HttpClient() { BaseAddress = new Uri(DomainHelper.GetDomain()) });
services.AddMvc();
}
// This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
{
DomainHelper = new WebDomainHelper(app.ApplicationServices.GetRequiredService());
app.UseHttpsRedirection();
app.UseStaticFiles();
app.UseRouting();
app.UseEndpoints(
endpoints =>
{
endpoints.MapControllerRoute("default", "{controller=Account}/{action=Index}/{id?}");
}
);
}
}
public class WebDomainHelper
{
IHttpContextAccessor ContextAccessor;
public WebDomainHelper(IHttpContextAccessor contextAccessor)
{
ContextAccessor = contextAccessor;
}
///
/// Get domain name
///
public string GetDomain()
{
string serverURL;
try
{
serverURL = $"{ContextAccessor.HttpContext.Request.Scheme}://{ContextAccessor.HttpContext.Request.Host.Value}/";
}
catch
{
serverURL = string.Empty;
}
return serverURL;
}
}