How to access server variables in ASP.Net Core 2.x

I've found Mark G's reference link very useful.

I've configure the middleware with ForwardedHeadersOptions to forward the X-Forwarded-For and X-Forwarded-Proto headers in Startup.ConfigureServices.

Here is my Startup.cs code file:

ConfigureServices

public void ConfigureServices(IServiceCollection services)
{
    services.AddDbContext<ApplicationDbContext>(options =>
           options.UseSqlServer(Configuration.GetConnectionString("DefaultConnection")));

    services.AddIdentity<ApplicationUser, IdentityRole>()
            .AddEntityFrameworkStores<ApplicationDbContext>()
            .AddDefaultTokenProviders();

    services.AddIdentityServer()
            .AddDeveloperSigningCredential()
            .AddInMemoryPersistedGrants()
            .AddInMemoryIdentityResources(Config.GetIdentityResources())
            .AddInMemoryApiResources(Config.GetApiResources())
            .AddInMemoryClients(Config.GetClients())
            .AddAspNetIdentity<ApplicationUser>();

    services.AddCors(options =>
    {
        options.AddPolicy("AllowClient",
                   builder => builder.WithOrigins("http://**.asyncsol.com", "http://*.asyncsol.com", "http://localhost:10761", "https://localhost:44335")
                                  .AllowAnyHeader()
                                  .AllowAnyMethod());
    });

    services.AddMvc();
    /* The relevant part for Forwarded Headers */
    services.Configure<ForwardedHeadersOptions>(options =>
    {
        options.ForwardedHeaders =
            ForwardedHeaders.XForwardedFor | ForwardedHeaders.XForwardedProto;
    });

    services.AddAuthentication(options =>
    {
        options.DefaultAuthenticateScheme = JwtBearerDefaults.AuthenticationScheme;
        options.DefaultChallengeScheme = JwtBearerDefaults.AuthenticationScheme;
    })
    .AddJwtBearer(options =>
    {
        // base-address of your identityserver
        //options.Authority = "http://server.asyncsol.com/";
        options.Authority = "http://localhost:52718/";

        // name of the API resource
        options.Audience = "api1";

        options.RequireHttpsMetadata = false;
    });
}

Configure

public void Configure(IApplicationBuilder app, IHostingEnvironment env)
{
    /* The relevant part for Forwarded Headers */
    app.UseForwardedHeaders();
    if (env.IsDevelopment())
    {
        app.UseDeveloperExceptionPage();
    }
    app.UseIdentityServer();
    app.UseAuthentication();
    app.UseCors("AllowAll");
    app.UseMvc(routes =>
    {
        routes.MapRoute(
            name: "areas",
            template: "{area:exists}/{controller=Home}/{action=Index}/{id?}"
        );
        routes.MapRoute(
            name: "default",
            template: "{controller=Home}/{action=Index}/{id?}");
    });
}

Usage at a Controller

public IEnumerable<string> Get()
{
    string ip = Response.HttpContext.Connection.RemoteIpAddress.ToString();

    //https://en.wikipedia.org/wiki/Localhost
    //127.0.0.1    localhost
    //::1          localhost
    if (ip == "::1")
    {
        ip = Dns.GetHostEntry(Dns.GetHostName()).AddressList[2].ToString();
    }

    return new string[] { ip.ToString() };
}

So, If I'm running on my localhost environment it shows my IPv4 system IP Address.
If I'm running my server on azure it shows my Host Name / IP Address.

Conclusion:

I've found my answer in Mark G comment Forwarded Headers Middleware

You can use HttpContext.Connection to get information about the connection (IP etc)

https://learn.microsoft.com/en-us/dotnet/api/microsoft.aspnetcore.http.httpcontext.connection?view=aspnetcore-2.1

https://learn.microsoft.com/en-us/dotnet/api/microsoft.aspnetcore.http.connectioninfo.remoteipaddress?view=aspnetcore-2.1#Microsoft_AspNetCore_Http_ConnectionInfo_RemoteIpAddress