Adds samesite

Author: jkotalik

src/Microsoft.AspNetCore.Http/Internal/ResponseCookies.cs

@@ -130,7 +130,8 @@ public void Delete(string key, CookieOptions options)
                 Domain = options.Domain,
                 Expires = new DateTime(1970, 1, 1, 0, 0, 0, DateTimeKind.Utc),
                 Secure = options.Secure,
-                HttpOnly = options.HttpOnly
+                HttpOnly = options.HttpOnly,
+                SameSite = options.SameSite
             });
         }
     }

test/Microsoft.AspNetCore.Http.Tests/ResponseCookiesTest.cs

@@ -41,7 +41,8 @@ public void DeleteCookieWithCookieOptionsShouldKeepPropertiesOfCookieOptions()
                 HttpOnly = true,
                 Path = "/",
                 Expires = time,
-                Domain = "example.com"
+                Domain = "example.com",
+                SameSite = SameSiteMode.Lax
             };
 
             cookies.Delete(testcookie, options);
@@ -53,6 +54,7 @@ public void DeleteCookieWithCookieOptionsShouldKeepPropertiesOfCookieOptions()
             Assert.Contains("expires=Thu, 01 Jan 1970 00:00:00 GMT", cookieHeaderValues[0]);
             Assert.Contains("secure", cookieHeaderValues[0]);
             Assert.Contains("httponly", cookieHeaderValues[0]);
+            Assert.Contains("samesite", cookieHeaderValues[0]);
         }
 
         [Fact]