contact/Startup.cs

using System;
using System.IO;
using contact.Services;
using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.DataProtection;
using Microsoft.AspNetCore.Hosting;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;

namespace contact
{
    public class Startup
    {
        public Startup(IConfiguration configuration)
        {
            Configuration = configuration;
        }

        public IConfiguration Configuration { get; }

        public void ConfigureServices(IServiceCollection services)
        {            
            services.AddRazorPages();
            services.AddSingleton<MailSender>();

            services.AddHttpClient("sockeye", client =>
            {
                client.Timeout = TimeSpan.FromSeconds(15);
            });

            //Antiforgery tokens on the forms are encrypted with Data Protection keys. The service account has no
            //home directory, so without this the keys live only in memory and every restart breaks forms that
            //visitors already have open. Set DataProtection:KeyPath on the server (systemd StateDirectory=contact).
            var keyPath = Configuration["DataProtection:KeyPath"];
            if (!string.IsNullOrWhiteSpace(keyPath))
            {
                services.AddDataProtection()
                    .SetApplicationName("contact")
                    .PersistKeysToFileSystem(new DirectoryInfo(keyPath));
            }
        }

        public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
        {
            if (env.IsDevelopment())
            {
                app.UseDeveloperExceptionPage();
            }
            else
            {
                app.UseExceptionHandler("/Error");
            }

            app.UseStaticFiles();
            app.UseRouting();
            app.UseEndpoints(endpoints =>
            {
                endpoints.MapControllers();
                endpoints.MapRazorPages();
            });
        }
    }
}