* Return old cookie token

src/Microsoft.AspNet.Antiforgery/DefaultAntiforgery.cs

@@ -67,7 +67,10 @@ namespace Microsoft.AspNet.Antiforgery
             CheckSSLConfig(context);
 
             var tokenSet = GetTokensInternal(context);
-            SaveCookieTokenAndHeader(context, tokenSet.CookieToken);
+            if (tokenSet.IsNewCookieToken)
+            {
+                SaveCookieTokenAndHeader(context, tokenSet.CookieToken);
+            }
             return Serialize(tokenSet);
         }
 
@@ -226,8 +229,9 @@ namespace Microsoft.AspNet.Antiforgery
             return new AntiforgeryTokenSetInternal()
             {
                 // Note : The new cookie would be null if the old cookie is valid.
-                CookieToken = newCookieToken,
-                FormToken = formToken
+                CookieToken = cookieToken,
+                FormToken = formToken,
+                IsNewCookieToken = newCookieToken != null
             };
         }
 
@@ -243,6 +247,8 @@ namespace Microsoft.AspNet.Antiforgery
             public AntiforgeryToken FormToken { get; set; }
 
             public AntiforgeryToken CookieToken { get; set; }
+
+            public bool IsNewCookieToken { get; set; }
         }
     }
 }

test/Microsoft.AspNet.Antiforgery.Test/DefaultAntiforgeryTest.cs

@@ -313,10 +313,51 @@ namespace Microsoft.AspNet.Antiforgery
             var tokenset = antiforgery.GetTokens(context.HttpContext);
 
             // Assert
-            Assert.Null(tokenset.CookieToken);
+            Assert.Equal("serialized-old-cookie-token", tokenset.CookieToken);
             Assert.Equal("serialized-form-token", tokenset.FormToken);
         }
 
+        [Fact]
+        public void GetAndStoreTokens_ExistingValidCookieToken_NotOverriden()
+        {
+            // Arrange
+            var context = CreateMockContext(
+                new AntiforgeryOptions(),
+                useOldCookie: true,
+                isOldCookieValid: true);
+            var antiforgery = GetAntiforgery(context);
+
+            // Act
+            var tokenSet = antiforgery.GetAndStoreTokens(context.HttpContext);
+
+            // Assert
+            // We shouldn't have saved the cookie because it already existed.
+            context.TokenStore.Verify(t => t.SaveCookieToken(It.IsAny<HttpContext>(), It.IsAny<AntiforgeryToken>()), Times.Never);
+            
+            Assert.Equal("serialized-old-cookie-token", tokenSet.CookieToken);
+            Assert.Equal("serialized-form-token", tokenSet.FormToken);
+        }
+
+        [Fact]
+        public void GetAndStoreTokens_NoExistingCookieToken_Saved()
+        {
+            // Arrange
+            var context = CreateMockContext(
+                new AntiforgeryOptions(),
+                useOldCookie: false,
+                isOldCookieValid: false);
+            var antiforgery = GetAntiforgery(context);
+
+            // Act
+            var tokenSet = antiforgery.GetAndStoreTokens(context.HttpContext);
+
+            // Assert
+            context.TokenStore.Verify(t => t.SaveCookieToken(It.IsAny<HttpContext>(), It.IsAny<AntiforgeryToken>()), Times.Once);
+
+            Assert.Equal("serialized-new-cookie-token", tokenSet.CookieToken);
+            Assert.Equal("serialized-form-token", tokenSet.FormToken);
+        }
+
         [Fact]
         public void ValidateTokens_FromInvalidStrings_Throws()
         {
@@ -533,6 +574,8 @@ namespace Microsoft.AspNet.Antiforgery
                           .Returns(formToken);
             mockSerializer.Setup(o => o.Deserialize(testTokenSet.OldCookieTokenString))
                           .Returns(oldCookieToken);
+            mockSerializer.Setup(o => o.Serialize(oldCookieToken))
+                          .Returns(testTokenSet.OldCookieTokenString);
             mockSerializer.Setup(o => o.Serialize(newCookieToken))
                           .Returns(testTokenSet.NewCookieTokenString);
             return mockSerializer;
@@ -549,7 +592,7 @@ namespace Microsoft.AspNet.Antiforgery
 
             var mockSerializer = GetTokenSerializer(testTokenSet);
 
-            var mockTokenStore = GetTokenStore(httpContext, testTokenSet);
+            var mockTokenStore = GetTokenStore(httpContext, testTokenSet, !useOldCookie);
 
             var mockGenerator = new Mock<IAntiforgeryTokenGenerator>(MockBehavior.Strict);
             mockGenerator