Enable same-origin credentials by default. Add E2E test to show they can be sent to different-origin domains too.

src/Microsoft.AspNetCore.Blazor.Browser.JS/src/Services/Http.ts

@@ -15,7 +15,7 @@ async function sendAsync(id: number, method: string, requestUri: string, body: s
   let response: Response;
   let responseText: string;
 
-  const requestInit = fetchArgs || {};
+  const requestInit: RequestInit = fetchArgs || {};
   requestInit.method = method;
   requestInit.body = body || undefined;
 

src/Microsoft.AspNetCore.Blazor.Browser/Http/BrowserHttpMessageHandler.cs

@@ -17,6 +17,13 @@ namespace Microsoft.AspNetCore.Blazor.Browser.Http
     /// </summary>
     public class BrowserHttpMessageHandler : HttpMessageHandler
     {
+        /// <summary>
+        /// Gets or sets the default value of the 'credentials' option on outbound HTTP requests.
+        /// Defaults to <see cref="FetchCredentialsOption.SameOrigin"/>.
+        /// </summary>
+        public static FetchCredentialsOption DefaultCredentials { get; set; }
+            = FetchCredentialsOption.SameOrigin;
+
         static object _idLock = new object();
         static int _nextRequestId = 0;
         static IDictionary<int, TaskCompletionSource<HttpResponseMessage>> _pendingRequests
@@ -47,7 +54,7 @@ namespace Microsoft.AspNetCore.Blazor.Browser.Http
                 request.RequestUri,
                 request.Content == null ? null : await GetContentAsString(request.Content),
                 SerializeHeadersAsJson(request),
-                fetchArgs);
+                fetchArgs ?? CreateDefaultFetchArgs());
 
             return await tcs.Task;
         }
@@ -93,6 +100,26 @@ namespace Microsoft.AspNetCore.Blazor.Browser.Http
             }
         }
 
+        private static object CreateDefaultFetchArgs()
+            => new { credentials = GetDefaultCredentialsString() };
+
+        private static object GetDefaultCredentialsString()
+        {
+            // See https://developer.mozilla.org/en-US/docs/Web/API/Request/credentials for
+            // standard values and meanings
+            switch (DefaultCredentials)
+            {
+                case FetchCredentialsOption.Omit:
+                    return "omit";
+                case FetchCredentialsOption.SameOrigin:
+                    return "same-origin";
+                case FetchCredentialsOption.Include:
+                    return "include";
+                default:
+                    throw new ArgumentException($"Unknown credentials option '{DefaultCredentials}'.");
+            }
+        }
+
         // Keep in sync with TypeScript class in Http.ts
         private class ResponseDescriptor
         {

src/Microsoft.AspNetCore.Blazor.Browser/Http/FetchCredentialsOption.cs

@@ -0,0 +1,28 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+namespace Microsoft.AspNetCore.Blazor.Browser.Http
+{
+    /// <summary>
+    /// Specifies a value for the 'credentials' option on outbound HTTP requests.
+    /// </summary>
+    public enum FetchCredentialsOption
+    {
+        /// <summary>
+        /// Advises the browser never to send credentials (such as cookies or HTTP auth headers).
+        /// </summary>
+        Omit,
+
+        /// <summary>
+        /// Advises the browser to send credentials (such as cookies or HTTP auth headers)
+        /// only if the target URL is on the same origin as the calling application.
+        /// </summary>
+        SameOrigin,
+
+        /// <summary>
+        /// Advises the browser to send credentials (such as cookies or HTTP auth headers)
+        /// even for cross-origin requests.
+        /// </summary>
+        Include,
+    }
+}

test/Microsoft.AspNetCore.Blazor.E2ETest/Infrastructure/BrowserFixture.cs

@@ -15,6 +15,8 @@ namespace Microsoft.AspNetCore.Blazor.E2ETest.Infrastructure
         public BrowserFixture()
         {
             var opts = new ChromeOptions();
+
+            // Comment this out if you want to watch or interact with the browser (e.g., for debugging)
             opts.AddArgument("--headless");
 
             // On Windows/Linux, we don't need to set opts.BinaryLocation

test/Microsoft.AspNetCore.Blazor.E2ETest/Tests/HttpClientTest.cs

@@ -106,6 +106,38 @@ namespace Microsoft.AspNetCore.Blazor.E2ETest.Tests
             Assert.EndsWith("/test-referrer", _responseBody.Text);
         }
 
+        [Fact]
+        public void CanSendAndReceiveCookies()
+        {
+            var app = MountTestComponent<CookieCounterComponent>();
+            var deleteButton = app.FindElement(By.Id("delete"));
+            var incrementButton = app.FindElement(By.Id("increment"));
+            app.FindElement(By.TagName("input")).SendKeys(_apiServerFixture.RootUri.ToString());
+
+            // Ensure we're starting from a clean state
+            deleteButton.Click();
+            Assert.Equal("Reset completed", WaitAndGetResponseText());
+
+            // Observe that subsequent requests manage to preserve state via cookie
+            incrementButton.Click();
+            Assert.Equal("Counter value is 1", WaitAndGetResponseText());
+            incrementButton.Click();
+            Assert.Equal("Counter value is 2", WaitAndGetResponseText());
+
+            // Verify that attempting to delete a cookie actually works
+            deleteButton.Click();
+            Assert.Equal("Reset completed", WaitAndGetResponseText());
+            incrementButton.Click();
+            Assert.Equal("Counter value is 1", WaitAndGetResponseText());
+
+            string WaitAndGetResponseText()
+            {
+                new WebDriverWait(Browser, TimeSpan.FromSeconds(30)).Until(
+                    driver => driver.FindElement(By.Id("response-text")) != null);
+                return app.FindElement(By.Id("response-text")).Text;
+            }
+        }
+
         private void IssueRequest(string requestMethod, string relativeUri, string requestBody = null)
         {
             var targetUri = new Uri(_apiServerFixture.RootUri, relativeUri);

test/testapps/BasicTestApp/HttpClientTest/CookieCounterComponent.cshtml

@@ -0,0 +1,38 @@
+@inject System.Net.Http.HttpClient Http
+
+<h1>Cookie counter</h1>
+<p>The server increments the count by one on each request.</p>
+<p>TestServer base URL: <input @bind(testServerBaseUrl) /></p>
+<button id="delete" @onclick(DeleteCookie)>Delete cookie</button>
+<button id="increment" @onclick(GetAndIncrementCounter)>Get and increment current value</button>
+
+@if (!requestInProgress)
+{
+    <p id="response-text">@responseText</p>
+}
+
+@functions
+{
+    bool requestInProgress = false;
+    string testServerBaseUrl;
+    string responseText;
+
+    async void DeleteCookie()
+    {
+        await DoRequest("api/cookie/reset");
+        StateHasChanged();
+    }
+
+    async void GetAndIncrementCounter()
+    {
+        await DoRequest("api/cookie/increment");
+        StateHasChanged();
+    }
+
+    async Task DoRequest(string url)
+    {
+        requestInProgress = true;
+        responseText = await Http.GetStringAsync(testServerBaseUrl + url);
+        requestInProgress = false;
+    }
+}

test/testapps/BasicTestApp/Program.cs

@@ -1,6 +1,7 @@
 // Copyright (c) .NET Foundation. All rights reserved.
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
+using Microsoft.AspNetCore.Blazor.Browser.Http;
 using Microsoft.AspNetCore.Blazor.Browser.Interop;
 using Microsoft.AspNetCore.Blazor.Browser.Rendering;
 using Microsoft.AspNetCore.Blazor.Components;
@@ -12,6 +13,10 @@ namespace BasicTestApp
     {
         static void Main(string[] args)
         {
+            // Needed because the test server runs on a different port than the client app,
+            // and we want to test sending/receiving cookies undering this config
+            BrowserHttpMessageHandler.DefaultCredentials = FetchCredentialsOption.Include;
+
             // Signal to tests that we're ready
             RegisteredFunction.Invoke<object>("testReady");
         }

test/testapps/BasicTestApp/wwwroot/index.html

@@ -22,6 +22,7 @@
       <option value="BasicTestApp.TextOnlyComponent">Plain text</option>
       <option value="BasicTestApp.HierarchicalImportsTest.Subdir.ComponentUsingImports">Imports statement</option>
       <option value="BasicTestApp.HttpClientTest.HttpRequestsComponent">HttpClient tester</option>
+      <option value="BasicTestApp.HttpClientTest.CookieCounterComponent">HttpClient cookies</option>
       <option value="BasicTestApp.BindCasesComponent">@bind cases</option>
       <option value="BasicTestApp.ExternalContentPackage">External content package</option>
       <option value="BasicTestApp.SvgComponent">SVG</option>

test/testapps/TestServer/Controllers/CookieController.cs

@@ -0,0 +1,32 @@
+using Microsoft.AspNetCore.Cors;
+using Microsoft.AspNetCore.Mvc;
+
+namespace TestServer.Controllers
+{
+    [Route("api/[controller]/[action]")]
+    [EnableCors("AllowAll")] // Only because the test client apps runs on a different origin
+    public class CookieController : Controller
+    {
+        const string cookieKey = "test-counter-cookie";
+
+        public string Reset()
+        {
+            Response.Cookies.Delete(cookieKey);
+            return "Reset completed";
+        }
+
+        public string Increment()
+        {
+            var counter = 0;
+            if (Request.Cookies.TryGetValue(cookieKey, out var incomingValue))
+            {
+                counter = int.Parse(incomingValue);
+            }
+
+            counter++;
+            Response.Cookies.Append(cookieKey, counter.ToString());
+
+            return $"Counter value is {counter}";
+        }
+    }
+}

test/testapps/TestServer/Startup.cs

@@ -20,14 +20,7 @@ namespace TestServer
             services.AddMvc();
             services.AddCors(options =>
             {
-                options.AddPolicy("AllowAll", builder =>
-                {
-                    builder
-                        .AllowAnyOrigin()
-                        .AllowAnyHeader()
-                        .AllowAnyMethod()
-                        .WithExposedHeaders("MyCustomHeader");
-                });
+                options.AddPolicy("AllowAll", _ => { /* Controlled below */ });
             });
         }
 
@@ -39,7 +32,32 @@ namespace TestServer
                 app.UseDeveloperExceptionPage();
             }
 
+            AllowCorsForAnyLocalhostPort(app);
             app.UseMvc();
         }
+
+        private static void AllowCorsForAnyLocalhostPort(IApplicationBuilder app)
+        {
+            // It's not enough just to return "Access-Control-Allow-Origin: *", because
+            // browsers don't allow wildcards in conjunction with credentials. So we must
+            // specify explicitly which origin we want to allow.
+            app.Use((context, next) =>
+            {
+                if (context.Request.Headers.TryGetValue("origin", out var incomingOriginValue))
+                {
+                    var origin = incomingOriginValue.ToArray()[0];
+                    if (origin.StartsWith("http://localhost:") || origin.StartsWith("http://127.0.0.1:"))
+                    {
+                        context.Response.Headers.Add("Access-Control-Allow-Origin", origin);
+                        context.Response.Headers.Add("Access-Control-Allow-Credentials", "true");
+                        context.Response.Headers.Add("Access-Control-Allow-Methods", "HEAD,GET,PUT,POST,DELETE,OPTIONS");
+                        context.Response.Headers.Add("Access-Control-Allow-Headers", "Content-Type,TestHeader,another-header");
+                        context.Response.Headers.Add("Access-Control-Expose-Headers", "MyCustomHeader,TestHeader,another-header");
+                    }
+                }
+
+                return next();
+            });
+        }
     }
 }