Solving SameSiteMode issue that some Chrome users are seeing.

XeroOAuth2Sample-MVC-PKCE/XeroOAuth2Sample-MVC-PKCE/Extensions/SameSiteHandlingExtensions.cs

@@ -0,0 +1,73 @@
+using Microsoft.AspNetCore.Builder;
+using Microsoft.AspNetCore.Http;
+using Microsoft.Extensions.DependencyInjection;
+
+namespace XeroOAuth2Sample_MVC_PKCE.Extensions
+{
+    // Copied from https://github.com/IdentityServer/IdentityServer4/blob/main/src/IdentityServer4/host/Extensions/SameSiteHandlingExtensions.cs on https://github.com/IdentityServer/IdentityServer4/commit/e581c13c0ba0234fbc253f918f7b1d620bf35734
+    // Also copied from https://devblogs.microsoft.com/aspnet/upcoming-samesite-cookie-changes-in-asp-net-and-asp-net-core/
+    public static class SameSiteHandlingExtensions
+    {
+        public static IServiceCollection AddSameSiteCookiePolicy(this IServiceCollection services)
+        {
+            services.Configure<CookiePolicyOptions>(options =>
+            {
+                options.MinimumSameSitePolicy = SameSiteMode.Unspecified;
+                options.OnAppendCookie = cookieContext => 
+                    CheckSameSite(cookieContext.Context, cookieContext.CookieOptions);
+                options.OnDeleteCookie = cookieContext => 
+                    CheckSameSite(cookieContext.Context, cookieContext.CookieOptions);
+            });
+
+            return services;
+        }
+
+        private static void CheckSameSite(HttpContext httpContext, CookieOptions options)
+        {
+            if (options.SameSite == SameSiteMode.None)
+            {
+                var userAgent = httpContext.Request.Headers["User-Agent"].ToString();
+                if (!httpContext.Request.IsHttps || DisallowsSameSiteNone(userAgent))
+                {
+                    // For .NET Core < 3.1 set SameSite = (SameSiteMode)(-1)
+                    options.SameSite = SameSiteMode.Unspecified;
+                }
+            }
+        }
+
+        private static bool DisallowsSameSiteNone(string userAgent)
+        {
+            // Cover all iOS based browsers here. This includes:
+            // - Safari on iOS 12 for iPhone, iPod Touch, iPad
+            // - WkWebview on iOS 12 for iPhone, iPod Touch, iPad
+            // - Chrome on iOS 12 for iPhone, iPod Touch, iPad
+            // All of which are broken by SameSite=None, because they use the iOS networking stack
+            if (userAgent.Contains("CPU iPhone OS 12") || userAgent.Contains("iPad; CPU OS 12"))
+            {
+                return true;
+            }
+
+            // Cover Mac OS X based browsers that use the Mac OS networking stack. This includes:
+            // - Safari on Mac OS X.
+            // This does not include:
+            // - Chrome on Mac OS X
+            // Because they do not use the Mac OS networking stack.
+            if (userAgent.Contains("Macintosh; Intel Mac OS X 10_14") && 
+                userAgent.Contains("Version/") && userAgent.Contains("Safari"))
+            {
+                return true;
+            }
+
+            // Cover Chrome 50-69, because some versions are broken by SameSite=None, 
+            // and none in this range require it.
+            // Note: this covers some pre-Chromium Edge versions, 
+            // but pre-Chromium Edge does not require SameSite=None.
+            if (userAgent.Contains("Chrome/5") || userAgent.Contains("Chrome/6"))
+            {
+                return true;
+            }
+
+            return false;
+        }
+    }
+}

XeroOAuth2Sample-MVC-PKCE/XeroOAuth2Sample-MVC-PKCE/Startup.cs

@@ -31,6 +31,8 @@ public Startup(IConfiguration configuration)
         // This method gets called by the runtime. Use this method to add services to the container.
         public void ConfigureServices(IServiceCollection services)
         {
+            services.AddSameSiteCookiePolicy();
+
             services.AddHttpClient();
 
             services.TryAddSingleton(new XeroConfiguration