Add configure delegate for CookieOptions

- allows configuration of CookieOptions such as SameSite without explicit duplication of the option on AntiforgeryOptions

src/Microsoft.AspNetCore.Antiforgery/AntiforgeryOptions.cs

@@ -47,18 +47,30 @@ namespace Microsoft.AspNetCore.Antiforgery
         }
 
         /// <summary>
+        /// This is obsolete and will be removed in a future version.
+        /// The recommended alternative is to use ConfigureCookieOptions.
         /// The path set on the cookie. If set to <c>null</c>, the "path" attribute on the cookie is set to the current
         /// request's <see cref="HttpRequest.PathBase"/> value. If the value of <see cref="HttpRequest.PathBase"/> is
         /// <c>null</c> or empty, then the "path" attribute is set to the value of <see cref="CookieOptions.Path"/>.
         /// </summary>
+        [Obsolete("This is obsolete and will be removed in a future version. The recommended alternative is to use ConfigureCookieOptions.")]
         public PathString? CookiePath { get; set; }
 
         /// <summary>
-        /// The domain set on the cookie. By default its <c>null</c> which results in the "domain" attribute not being
+        /// This is obsolete and will be removed in a future version.
-        /// set.
+        /// The recommended alternative is to use ConfigureCookieOptions.
+        /// The domain set on the cookie. By default its <c>null</c> which results in the "domain" attribute not being set.
         /// </summary>
+        [Obsolete("This is obsolete and will be removed in a future version. The recommended alternative is to use ConfigureCookieOptions.")]
         public string CookieDomain { get; set; }
 
+        /// <summary>
+        /// Configures the <see cref="CookieOptions"/> of the antiforgery cookies. Without additional configuration, the 
+        /// default values antiforgery cookie options are true for <see cref="CookieOptions.HttpOnly"/>, null for
+        /// <see cref="CookieOptions.Domain"/> and <see cref="SameSiteMode.Strict"/> for <see cref="CookieOptions.SameSite"/>.
+        /// </summary>
+        public Action<HttpContext, CookieOptions> ConfigureCookieOptions { get; set; }
+
         /// <summary>
         /// Specifies the name of the antiforgery token field that is used by the antiforgery system.
         /// </summary>

src/Microsoft.AspNetCore.Antiforgery/Internal/DefaultAntiforgeryTokenStore.cs

@@ -69,34 +69,34 @@ namespace Microsoft.AspNetCore.Antiforgery.Internal
             Debug.Assert(httpContext != null);
             Debug.Assert(token != null);
 
-            var options = new CookieOptions();
+            var options = new CookieOptions
-            options.HttpOnly = true;
-            options.Domain = _options.CookieDomain;
-            // Note: don't use "newCookie.Secure = _options.RequireSSL;" since the default
-            // value of newCookie.Secure is populated out of band.
-            if (_options.RequireSsl)
             {
-                options.Secure = true;
+                HttpOnly = true,
-            }
+#pragma warning disable 618
-            SetCookiePath(httpContext, options);
+                Domain = _options.CookieDomain,
+#pragma warning restore 618
+                SameSite = SameSiteMode.Strict,
+                Secure = _options.RequireSsl
+            };
 
-            httpContext.Response.Cookies.Append(_options.CookieName, token, options);
+#pragma warning disable 618
-        }
-
-        private void SetCookiePath(HttpContext httpContext, CookieOptions cookieOptions)
-        {
             if (_options.CookiePath != null)
             {
-                cookieOptions.Path = _options.CookiePath.ToString();
+                options.Path = _options.CookiePath.ToString();
             }
+#pragma warning restore 618
             else
             {
                 var pathBase = httpContext.Request.PathBase.ToString();
                 if (!string.IsNullOrEmpty(pathBase))
                 {
-                    cookieOptions.Path = pathBase;
+                    options.Path = pathBase;
                 }
             }
+
+            _options.ConfigureCookieOptions?.Invoke(httpContext, options);
+
+            httpContext.Response.Cookies.Append(_options.CookieName, token, options);
         }
     }
 }

test/Microsoft.AspNetCore.Antiforgery.Test/Internal/DefaultAntiforgeryTokenStoreTest.cs

@@ -311,7 +311,7 @@ namespace Microsoft.AspNetCore.Antiforgery.Internal
         }
 
         [Fact]
-        public void SaveCookieToken_NonNullAntiforgeryOptionsCookiePath_UsesOptionsCookiePath()
+        public void SaveCookieToken_NonNullAntiforgeryOptionsConfigureCookieOptionsPath_UsesCookieOptionsPath()
         {
             // Arrange
             var expectedCookiePath = "/";
@@ -330,7 +330,7 @@ namespace Microsoft.AspNetCore.Antiforgery.Internal
                 .Returns("/index.html");
             var options = new AntiforgeryOptions();
             options.CookieName = _cookieName;
-            options.CookiePath = expectedCookiePath;
+            options.ConfigureCookieOptions = (context, cookieOptions) => cookieOptions.Path = expectedCookiePath;
             var tokenStore = new DefaultAntiforgeryTokenStore(new TestOptionsManager(options));
 
             // Act
@@ -346,7 +346,7 @@ namespace Microsoft.AspNetCore.Antiforgery.Internal
         }
 
         [Fact]
-        public void SaveCookieToken_NonNullAntiforgeryOptionsCookieDomain_UsesOptionsCookieDomain()
+        public void SaveCookieToken_NonNullAntiforgeryOptionsConfigureCookieOptionsDomain_UsesCookieOptionsDomain()
         {
             // Arrange
             var expectedCookieDomain = "microsoft.com";
@@ -364,7 +364,7 @@ namespace Microsoft.AspNetCore.Antiforgery.Internal
                 .Returns("/index.html");
             var options = new AntiforgeryOptions();
             options.CookieName = _cookieName;
-            options.CookieDomain = expectedCookieDomain;
+            options.ConfigureCookieOptions = (context, cookieOptions) => cookieOptions.Domain = expectedCookieDomain;
             var tokenStore = new DefaultAntiforgeryTokenStore(new TestOptionsManager(options));
 
             // Act