Normalize internationalized domain names when adding to CORS

Fixes https://github.com/aspnet/Home/issues/3353

src/Microsoft.AspNetCore.Cors/Infrastructure/CorsPolicyBuilder.cs

@@ -17,6 +17,7 @@ namespace Microsoft.AspNetCore.Cors.Infrastructure
         /// Creates a new instance of the <see cref="CorsPolicyBuilder"/>.
         /// </summary>
         /// <param name="origins">list of origins which can be added.</param>
+        /// <remarks> <see cref="WithOrigins(string[])"/> for details on normalizing the origin value.</remarks>
         public CorsPolicyBuilder(params string[] origins)
         {
             WithOrigins(origins);
@@ -36,16 +37,55 @@ namespace Microsoft.AspNetCore.Cors.Infrastructure
         /// </summary>
         /// <param name="origins">The origins that are allowed.</param>
         /// <returns>The current policy builder.</returns>
+        /// <remarks>
+        /// This method normalizes the origin value prior to adding it to <see cref="CorsPolicy.Origins"/> to match
+        /// the normalization performed by the browser on the value sent in the <c>ORIGIN</c> header.
+        /// <list type="bullet">
+        /// <item>
+        /// If the specified origin has an internationalized domain name (IDN), the punycoded value is used. If the origin
+        /// specifies a default port (e.g. 443 for HTTPS or 80 for HTTP), this will be dropped as part of normalization.
+        /// Finally, the scheme and punycoded host name are culture invariant lower cased before being added to the <see cref="CorsPolicy.Origins"/>
+        /// collection.
+        /// </item>
+        /// <item>
+        /// For all other origins, normalization involves performing a culture invariant lower casing of the host name.
+        /// </item>
+        /// </list>
+        /// </remarks>
         public CorsPolicyBuilder WithOrigins(params string[] origins)
         {
             foreach (var origin in origins)
             {
-                _policy.Origins.Add(origin.ToLowerInvariant());
+                var normalizedOrigin = GetNormalizedOrigin(origin);
+                _policy.Origins.Add(normalizedOrigin);
             }
 
             return this;
         }
 
+        internal static string GetNormalizedOrigin(string origin)
+        {
+            if (Uri.TryCreate(origin, UriKind.Absolute, out var uri) &&
+                (uri.Scheme == Uri.UriSchemeHttp || uri.Scheme == Uri.UriSchemeHttps) &&
+                !string.Equals(uri.IdnHost, uri.Host, StringComparison.Ordinal))
+            {
+                var builder = new UriBuilder(uri.Scheme.ToLowerInvariant(), uri.IdnHost.ToLowerInvariant());
+                if (!uri.IsDefaultPort)
+                {
+                    // Uri does not have a way to differentiate between a port value inferred by default (e.g. Port = 80 for http://www.example.com) and
+                    // a default port value that is specified (e.g. Port = 80 for http://www.example.com:80). Although the HTTP or FETCH spec does not say 
+                    // anything about including the default port as part of the Origin header, at the time of writing, browsers drop "default" port when navigating
+                    // and when sending the Origin header. All this goes to say, it appears OK to drop an explicitly specified port, 
+                    // if it is the default port when working with an IDN host.
+                    builder.Port = uri.Port;
+                }
+
+                return builder.Uri.GetComponents(UriComponents.SchemeAndServer, UriFormat.Unescaped);
+            }
+
+            return origin.ToLowerInvariant();
+        }
+
         /// <summary>
         /// Adds the specified <paramref name="headers"/> to the policy.
         /// </summary>
@@ -222,4 +262,4 @@ namespace Microsoft.AspNetCore.Cors.Infrastructure
             return this;
         }
     }
-}
+}

test/Microsoft.AspNetCore.Cors.Test/CorsPolicyBuilderTests.cs

@@ -1,4 +1,4 @@
-// Copyright (c) .NET Foundation. All rights reserved.
+// 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;
@@ -299,5 +299,85 @@ namespace Microsoft.AspNetCore.Cors.Infrastructure
             var corsPolicy = builder.Build();
             Assert.False(corsPolicy.SupportsCredentials);
         }
+
+        [Theory]
+        [InlineData("Some-String", "some-string")]
+        [InlineData("x:\\Test", "x:\\test")]
+        [InlineData("FTP://Some-url", "ftp://some-url")]
+        public void GetNormalizedOrigin_ReturnsLowerCasedValue_IfStringIsNotHttpOrHttpsUrl(string origin, string expected)
+        {
+            // Act
+            var normalizedOrigin = CorsPolicyBuilder.GetNormalizedOrigin(origin);
+
+            // Assert
+            Assert.Equal(expected, normalizedOrigin);
+        }
+
+        [Fact]
+        public void GetNormalizedOrigin_DoesNotAddPort_IfUriDoesNotSpecifyOne()
+        {
+            // Arrange
+            var origin = "http://www.example.com";
+
+            // Act
+            var normalizedOrigin = CorsPolicyBuilder.GetNormalizedOrigin(origin);
+
+            // Assert
+            Assert.Equal(origin, normalizedOrigin);
+        }
+
+        [Fact]
+        public void GetNormalizedOrigin_LowerCasesScheme()
+        {
+            // Arrange
+            var origin = "HTTP://www.example.com";
+
+            // Act
+            var normalizedOrigin = CorsPolicyBuilder.GetNormalizedOrigin(origin);
+
+            // Assert
+            Assert.Equal("http://www.example.com", normalizedOrigin);
+        }
+
+        [Fact]
+        public void GetNormalizedOrigin_LowerCasesHost()
+        {
+            // Arrange
+            var origin = "http://www.Example.Com";
+
+            // Act
+            var normalizedOrigin = CorsPolicyBuilder.GetNormalizedOrigin(origin);
+
+            // Assert
+            Assert.Equal("http://www.example.com", normalizedOrigin);
+        }
+
+        [Theory]
+        [InlineData("http://www.Example.com:80", "http://www.example.com:80")]
+        [InlineData("https://www.Example.com:8080", "https://www.example.com:8080")]
+        public void GetNormalizedOrigin_PreservesPort_ForNonIdnHosts(string origin, string expected)
+        {
+            // Act
+            var normalizedOrigin = CorsPolicyBuilder.GetNormalizedOrigin(origin);
+
+            // Assert
+            Assert.Equal(expected, normalizedOrigin);
+        }
+
+        [Theory]
+        [InlineData("http://Bücher.example", "http://xn--bcher-kva.example")]
+        [InlineData("http://Bücher.example.com:83", "http://xn--bcher-kva.example.com:83")]
+        [InlineData("https://example.қаз", "https://example.xn--80ao21a")]
+        [InlineData("http://😉.fm", "http://xn--n28h.fm")]
+        // Note that in following case, the default port (443 for HTTPS) is not preserved.
+        [InlineData("https://www.example.இந்தியா:443", "https://www.example.xn--xkc2dl3a5ee0h")]
+        public void GetNormalizedOrigin_ReturnsPunyCodedOrigin(string origin, string expected)
+        {
+            // Act
+            var normalizedOrigin = CorsPolicyBuilder.GetNormalizedOrigin(origin);
+
+            // Assert
+            Assert.Equal(expected, normalizedOrigin);
+        }
     }
-}
+}