From 1d2f4e8a5b86a5bacd5fe2d6c25026dbaf3ba460 Mon Sep 17 00:00:00 2001
From: WeebDataHoarder <weebdatahoarder@noreply.gammaspectra.live>
Date: Sun, 4 May 2025 20:21:53 +0200
Subject: [PATCH] challenge/context: use additional HTTP headers in challenge
 key generation if the challenge allows for it

---
 lib/challenge/data.go                      |  3 +++
 lib/challenge/key.go                       | 16 ++++++-------
 lib/challenge/preload-link/preload-link.go |  3 +++
 lib/challenge/register.go                  | 28 +++++++++++++++++++---
 4 files changed, 38 insertions(+), 12 deletions(-)

diff --git a/lib/challenge/data.go b/lib/challenge/data.go
index bb4936e..37faa4d 100644
--- a/lib/challenge/data.go
+++ b/lib/challenge/data.go
@@ -329,6 +329,9 @@ func (d *RequestData) ResponseHeaders(w http.ResponseWriter) {
 	//w.Header().Set("Accept-CH", "Sec-CH-UA, Sec-CH-UA-Platform")
 	//w.Header().Set("Critical-CH", "Sec-CH-UA, Sec-CH-UA-Platform")
 
+	// send Vary header to mark that response may vary based on Cookie values and other client headers
+	w.Header().Set("Vary", "Cookie, Accept, Accept-Encoding, Accept-Language, User-Agent")
+
 	if d.State.Settings().MainName != "" {
 		w.Header().Add("Via", fmt.Sprintf("%s %s@%s", d.r.Proto, d.State.Settings().MainName, d.State.Settings().MainVersion))
 	}
diff --git a/lib/challenge/key.go b/lib/challenge/key.go
index 6574246..d862918 100644
--- a/lib/challenge/key.go
+++ b/lib/challenge/key.go
@@ -52,15 +52,13 @@ func GetChallengeKeyForRequest(state StateInterface, reg *Registration, until ti
 	hasher.Write([]byte{0})
 
 	// specific headers
-	for _, k := range []string{
-		"Accept-Language",
-		// General browser information
-		"User-Agent",
-		// TODO: not sent in preload
-		//"Sec-Ch-Ua",
-		//"Sec-Ch-Ua-Platform",
-	} {
-		hasher.Write([]byte(r.Header.Get(k)))
+	for _, k := range reg.KeyHeaders {
+		hasher.Write([]byte(k))
+		hasher.Write([]byte{0})
+		for _, v := range r.Header.Values(k) {
+			hasher.Write([]byte(v))
+			hasher.Write([]byte{1})
+		}
 		hasher.Write([]byte{0})
 	}
 	hasher.Write([]byte{0})
diff --git a/lib/challenge/preload-link/preload-link.go b/lib/challenge/preload-link/preload-link.go
index 1acac99..b86df30 100644
--- a/lib/challenge/preload-link/preload-link.go
+++ b/lib/challenge/preload-link/preload-link.go
@@ -44,6 +44,9 @@ func FillRegistration(state challenge.StateInterface, reg *challenge.Registratio
 
 	reg.Class = challenge.ClassTransparent
 
+	// some of regular headers are not sent in default headers
+	reg.KeyHeaders = challenge.MinimalKeyHeaders
+
 	ob := challenge.NewAwaiter[string]()
 
 	reg.Object = ob
diff --git a/lib/challenge/register.go b/lib/challenge/register.go
index 25f8ad1..7707a5b 100644
--- a/lib/challenge/register.go
+++ b/lib/challenge/register.go
@@ -35,6 +35,24 @@ var idCounter Id
 // DefaultDuration TODO: adjust
 const DefaultDuration = time.Hour * 24 * 7
 
+var DefaultKeyHeaders = []string{
+	// General browser information
+	"User-Agent",
+	// Accept headers
+	"Accept-Language",
+	"Accept-Encoding",
+
+	// NOTE: not sent in preload
+	"Sec-Ch-Ua",
+	"Sec-Ch-Ua-Platform",
+}
+
+var MinimalKeyHeaders = []string{
+	"Accept-Language",
+	// General browser information
+	"User-Agent",
+}
+
 func (r Register) Create(state StateInterface, name string, pol policy.Challenge, replacer *strings.Replacer) (*Registration, Id, error) {
 	runtime, ok := Runtimes[pol.Runtime]
 	if !ok {
@@ -42,9 +60,10 @@ func (r Register) Create(state StateInterface, name string, pol policy.Challenge
 	}
 
 	reg := &Registration{
-		Name:     name,
-		Path:     path.Join(state.UrlPath(), "challenge", name),
-		Duration: pol.Duration,
+		Name:       name,
+		Path:       path.Join(state.UrlPath(), "challenge", name),
+		Duration:   pol.Duration,
+		KeyHeaders: DefaultKeyHeaders,
 	}
 
 	if reg.Duration == 0 {
@@ -126,6 +145,9 @@ type Registration struct {
 	Verify            VerifyFunc
 	VerifyProbability float64
 
+	// KeyHeaders The client headers used in key generation, in this order
+	KeyHeaders []string
+
 	// IssueChallenge Issues a challenge to a request.
 	// If Class is ClassTransparent and VerifyResult is !VerifyResult.Ok(), continue with other challenges
 	// TODO: have this return error as well