Move Antiforgery.GetHtml() to MVC as an extension

src/Microsoft.AspNetCore.Mvc.ViewFeatures/ViewFeatures/AntiforgeryExtensions.cs

@@ -0,0 +1,81 @@
+// 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 System;
+using System.IO;
+using System.Text.Encodings.Web;
+using Microsoft.AspNetCore.Antiforgery;
+using Microsoft.AspNetCore.Html;
+using Microsoft.AspNetCore.Http;
+
+namespace Microsoft.AspNetCore.Mvc.ViewFeatures
+{
+    public static class AntiforgeryExtensions
+    {
+        /// <summary>
+        /// Generates an &lt;input type="hidden"&gt; element for an antiforgery token.
+        /// </summary>
+        /// <param name="antiforgery">The <see cref="IAntiforgery"/> instance.</param>
+        /// <param name="httpContext">The <see cref="HttpContext"/> associated with the current request.</param>
+        /// <returns>
+        /// A <see cref="IHtmlContent"/> containing an &lt;input type="hidden"&gt; element. This element should be put
+        /// inside a &lt;form&gt;.
+        /// </returns>
+        /// <remarks>
+        /// This method has a side effect:
+        /// A response cookie is set if there is no valid cookie associated with the request.
+        /// </remarks>
+        public static IHtmlContent GetHtml(this IAntiforgery antiforgery, HttpContext httpContext)
+        {
+            if (antiforgery == null)
+            {
+                throw new ArgumentNullException(nameof(antiforgery));
+            }
+
+            if (httpContext == null)
+            {
+                throw new ArgumentNullException(nameof(httpContext));
+            }
+
+            var tokenSet = antiforgery.GetAndStoreTokens(httpContext);
+            return new InputContent(tokenSet);
+        }
+
+        private class InputContent : IHtmlContent
+        {
+            private readonly string _fieldName;
+            private readonly string _requestToken;
+
+            public InputContent(AntiforgeryTokenSet tokenSet)
+            {
+                _fieldName = tokenSet.FormFieldName;
+                _requestToken = tokenSet.RequestToken;
+            }
+
+            // Though _requestToken normally contains only US-ASCII letters, numbers, '-', and '_', must assume the
+            // IAntiforgeryTokenSerializer implementation has been overridden. Similarly, users may choose a
+            // _fieldName containing almost any character.
+            public void WriteTo(TextWriter writer, HtmlEncoder encoder)
+            {
+                var builder = writer as IHtmlContentBuilder;
+                if (builder != null)
+                {
+                    // If possible, defer encoding until we're writing to the response.
+                    // But there's little reason to keep this IHtmlContent instance around.
+                    builder
+                        .AppendHtml("<input name=\"")
+                        .Append(_fieldName)
+                        .AppendHtml("\" type=\"hidden\" value=\"")
+                        .Append(_requestToken)
+                        .AppendHtml("\" />");
+                }
+
+                writer.Write("<input name=\"");
+                encoder.Encode(writer, _fieldName);
+                writer.Write("\" type=\"hidden\" value=\"");
+                encoder.Encode(writer, _requestToken);
+                writer.Write("\" />");
+            }
+        }
+    }
+}

test/Microsoft.AspNetCore.Mvc.ViewFeatures.Test/ViewFeatures/AntiforgeryExtensionsTest.cs

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+// 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.Antiforgery;
+using Microsoft.AspNetCore.Http;
+using Microsoft.AspNetCore.Http.Internal;
+using Microsoft.AspNetCore.Mvc.TestCommon;
+using Moq;
+using Xunit;
+
+namespace Microsoft.AspNetCore.Mvc.ViewFeatures
+{
+    /// <summary>
+    /// Extension methods for <see cref="IAntiforgery"/>.
+    /// </summary>
+    public class AntiforgeryExtensionsTest
+    {
+        [Fact]
+        public void GetHtml_RendersInputField()
+        {
+            // Arrange
+            var antiforgery = new Mock<IAntiforgery>(MockBehavior.Strict);
+            var tokenSet = new AntiforgeryTokenSet("request-token", "cookie-token", "form-field", "header");
+            antiforgery
+                .Setup(a => a.GetAndStoreTokens(It.IsAny<HttpContext>()))
+                .Returns(tokenSet);
+
+            // Act
+            var inputElement = AntiforgeryExtensions.GetHtml(antiforgery.Object, new DefaultHttpContext());
+
+            // Assert
+            Assert.Equal(
+                @"<input name=""HtmlEncode[[form-field]]"" type=""hidden"" value=""HtmlEncode[[request-token]]"" />",
+                HtmlContentUtilities.HtmlContentToString(inputElement));
+        }
+    }
+}