feat: hack: support the "Partitioned" flag on VCAP_ID cookies

The `Partitioned` flag is used for cookies that are set on web sites
embedded via iframes. The cookie is then available only in combination
of the host site and the embedded site.

Golang's `http.Cookie` type does not yet support the `Partitioned`
flag, but Google Chrome is already testing mandatory support and
rejecting/omitting cookies without it for 1% of users via A/B roll-out.

The implementation wraps the `http.Cookie` and extends it with the
`Partitioned` field. This field is then used to forward the raw
cookie string when creating the derived VCAP_ID cookies for sticky
sessions.

Once the Golang standard library supports the `Partitioned` flag, this
wrapper can just be removed.

A test that checks the `Unparsed` section of the `http.Cookie` will
ensure that the tests will fail once the `Partitioned` flag is
supported by the Golang standard library.

proxy/round_tripper/proxy_round_tripper.go

@@ -10,6 +10,7 @@ import (
 	"net/http/httptrace"
 	"net/textproto"
 	"net/url"
+	"slices"
 	"strings"
 	"sync"
 	"time"
@@ -61,6 +62,20 @@ func GetRoundTripper(endpoint *route.Endpoint, roundTripperFactory RoundTripperF
 	return endpoint.RoundTripper()
 }
 
+type Cookie struct {
+	http.Cookie
+	// indicates, whether this cookie is partitioned. Relevant for embedding in iframes.
+	Partitioned bool
+}
+
+func (c *Cookie) String() string {
+	cookieString := c.Cookie.String()
+	if c.Partitioned {
+		return cookieString + "; Partitioned"
+	}
+	return cookieString
+}
+
 //go:generate counterfeiter -o fakes/fake_error_handler.go --fake-name ErrorHandler . errorHandler
 type errorHandler interface {
 	HandleError(utils.ProxyResponseWriter, error)
@@ -399,6 +414,7 @@ func setupStickySession(
 	maxAge := 0
 	sameSite := http.SameSite(0)
 	expiry := time.Time{}
+	partitioned := false
 
 	if responseContainsAuthNegotiateHeader && authNegotiateSticky {
 		maxAge = AuthNegotiateHeaderCookieMaxAgeInSeconds
@@ -414,6 +430,11 @@ func setupStickySession(
 				secure = v.Secure
 				sameSite = v.SameSite
 				expiry = v.Expires
+
+				// temporary workaround for "Partitioned" cookies, used in embedded websites (iframe),
+				// until Golang natively supports parsing the Partitioned flag.
+				// See also https://github.com/golang/go/issues/62490
+				partitioned = slices.Contains(v.Unparsed, "Partitioned")
 				break
 			}
 		}
@@ -433,15 +454,18 @@ func setupStickySession(
 			secure = true
 		}
 
-		vcapIDCookie := &http.Cookie{
-			Name:     VcapCookieId,
-			Value:    endpoint.PrivateInstanceId,
-			Path:     path,
-			MaxAge:   maxAge,
-			HttpOnly: true,
-			Secure:   secure,
-			SameSite: sameSite,
-			Expires:  expiry,
+		vcapIDCookie := &Cookie{
+			Cookie: http.Cookie{
+				Name:     VcapCookieId,
+				Value:    endpoint.PrivateInstanceId,
+				Path:     path,
+				MaxAge:   maxAge,
+				HttpOnly: true,
+				Secure:   secure,
+				SameSite: sameSite,
+				Expires:  expiry,
+			},
+			Partitioned: partitioned,
 		}
 
 		if v := vcapIDCookie.String(); v != "" {

proxy/round_tripper/proxy_round_tripper_test.go

@@ -993,7 +993,7 @@ var _ = Describe("ProxyRoundTripper", func() {
 
 			Context("when using sticky sessions", func() {
 				var (
-					sessionCookie *http.Cookie
+					sessionCookie *round_tripper.Cookie
 					endpoint1     *route.Endpoint
 					endpoint2     *route.Endpoint
 
@@ -1018,6 +1018,7 @@ var _ = Describe("ProxyRoundTripper", func() {
 						sessionCookie.Expires = time.Date(2020, 1, 1, 1, 0, 0, 0, time.UTC)
 						sessionCookie.Secure = true
 						sessionCookie.HttpOnly = true
+						sessionCookie.Partitioned = true
 					}
 
 					sessionCookie.Value, _ = uuid.GenerateUUID()
@@ -1026,9 +1027,11 @@ var _ = Describe("ProxyRoundTripper", func() {
 				}
 
 				setVCAPID := func(resp *http.Response) (response *http.Response) {
-					vcapCookie := http.Cookie{
-						Name:  round_tripper.VcapCookieId,
-						Value: "vcap-id-property-already-on-the-response",
+					vcapCookie := round_tripper.Cookie{
+						Cookie: http.Cookie{
+							Name:  round_tripper.VcapCookieId,
+							Value: "vcap-id-property-already-on-the-response",
+						},
 					}
 
 					if c := vcapCookie.String(); c != "" {
@@ -1072,8 +1075,10 @@ var _ = Describe("ProxyRoundTripper", func() {
 				}
 
 				BeforeEach(func() {
-					sessionCookie = &http.Cookie{
-						Name: StickyCookieKey, //JSESSIONID
+					sessionCookie = &round_tripper.Cookie{
+						Cookie: http.Cookie{
+							Name: StickyCookieKey, //JSESSIONID
+						},
 					}
 
 					endpoint1 = route.NewEndpoint(&route.EndpointOpts{
@@ -1365,10 +1370,15 @@ var _ = Describe("ProxyRoundTripper", func() {
 								newCookies := resp.Cookies()
 								Expect(newCookies).To(HaveLen(2))
 								Expect(newCookies[0].Raw).To(Equal(sessionCookie.String()))
+
+								// This should fail when Golang introduces parsing for the Partitioned flag on cookies.
+								// see https://github.com/golang/go/issues/62490
+								Expect(newCookies[0].Unparsed).To(Equal([]string{"Partitioned"}))
+
 								Expect(newCookies[1].Name).To(Equal(round_tripper.VcapCookieId))
 								Expect(newCookies[1].Value).To(Equal(cookies[1].Value)) // still pointing to the same app
-								Expect(sessionCookie.String()).To(ContainSubstring("Expires=Wed, 01 Jan 2020 01:00:00 GMT; HttpOnly; Secure; SameSite=Strict"))
-								Expect(newCookies[1].Raw).To(ContainSubstring("Expires=Wed, 01 Jan 2020 01:00:00 GMT; HttpOnly; Secure; SameSite=Strict"))
+								Expect(sessionCookie.String()).To(ContainSubstring("Expires=Wed, 01 Jan 2020 01:00:00 GMT; HttpOnly; Secure; SameSite=Strict; Partitioned"))
+								Expect(newCookies[1].Raw).To(ContainSubstring("Expires=Wed, 01 Jan 2020 01:00:00 GMT; HttpOnly; Secure; SameSite=Strict; Partitioned"))
 							})
 						})