fix(client): VK captcha new format, Android TLS, auto-solver improvements

Three intertwined fixes that together make the client usable again on
Android and against the new VK captcha flow that started 2026-06-25.

== Fix #182 — captcha parser for new VK error format ==
VK started returning a captcha-required error (error_code 14) at the
calls.getAnonymousToken step in a NEW shape that only carries:

    error_code, error_msg, is_enabled_captcha, redirect_uri

and notably NO captcha_sid and NO captcha_img. The previous parser
rejected this payload with "missing captcha_sid in captcha error data"
and returned nil, so the auth loop never reached the captcha solver
and just fell through to the next client_id — exactly the regression
reported in issue #182.

ParseVkCaptchaError now treats redirect_uri, captcha_sid, captcha_img
and error_msg as optional and only requires error_code plus at least
one solvable path (redirect_uri+session_token OR captcha_img/captcha_sid).
The new flow's request body no longer sends an empty captcha_sid when
only success_token is available.

Tests in captcha_parse_test.go cover:
  - new format without captcha_sid (issue #182 repro)
  - legacy format with captcha_sid + captcha_img
  - numeric captcha_sid
  - unsolvable payload returns nil
  - missing error_code returns nil

== Android TLS — embedded Mozilla CA bundle ==
VK switched *.vk.com to a certificate issued by HARICA TLS RSA Root
CA 2021 (a Greek CA added to the Mozilla trust store only in 2022).
The bogdanfinn/tls-client library leaves RootCAs as nil by default,
which makes Go fall back to x509.SystemCertPool() — and that pool is
EMPTY on Android apps (no /etc/ssl/certs/), so every HTTPS request
failed with:
    tls: failed to verify certificate: x509: certificate signed by unknown authority

A new client/ca_bundle.go helper loads a CA pool with the following
priority:
  1. SSL_CERT_FILE env var (if set)
  2. x509.SystemCertPool() (desktops/servers)
  3. Embedded Mozilla CA bundle (client/certs/cacert.pem, 189 KB,
     contains HARICA TLS RSA/ECC Root CA 2021)

The embedded bundle is the same one curl ships, downloaded from
https://curl.se/ca/cacert.pem. A VKTURN_INSECURE_TLS env var is
honored for emergency debugging (not exposed as a CLI flag —
production should always verify).

== Auto-captcha improvements ==
After reverse-engineering not_robot_captcha.js (878 KB), I found three
bugs in the existing inline captchaNotRobot.check flow that each
alone caused VK to return status:BOT:

  1. PoW hash was sent as bare hex. VK's JS produces:
         window.captchaPowResult = "v2." + btoa(JSON.stringify({hash, nonce}))
     Now solvePoW returns (hash, nonce) and formatPoWResult wraps them.

  2. debug_info was a random per-request MD5. VK's JS sends either
     window.vk.brlefapmjnpg or the hardcoded fallback
     "4045edac1cb2c18eff209dc09cd5e2e56475a13ed4615413a87618b3c6813f9a".
     Now uses the hardcoded fallback.

  3. captchaNotRobot.initSession was never called. VK's JS always calls
     it before settings; without it the server-side session state is
     not fully initialized. Now called as Step 0/4 in both
     callCaptchaNotRobot and callCaptchaNotRobotWithSliderPOC.

Also fixed:
  - connectionRtt was a constant [50,50,50,...] — now generated with
    realistic jitter (45-84ms baseline, occasional spikes).
  - connectionDownlink was a constant [9.5,9.5,...] — now generated
    with mild per-sample jitter.
  - check response is now logged (status, show_captcha_type, redirect)
    so future debugging is easier.

NOTE: even with all three fixes, VK still returns status:BOT when the
client runs from a datacenter IP or without a real browser. The reason
is browser_fp = FingerprintJS visitor_id (computed via canvas/webgl/
font fingerprinting in the browser) — this cannot be faked from Go
code. The next commit adds a Playwright-based solver that runs a real
headless Chromium to produce a valid browser_fp.

client/ca_bundle.go

@@ -0,0 +1,82 @@
+package main
+
+import (
+	"crypto/x509"
+	_ "embed"
+	"log"
+	"os"
+	"strings"
+)
+
+//go:embed certs/cacert.pem
+var mozillaCABundlePEM []byte
+
+// loadCABundle returns a *x509.CertPool that can verify VK (and any other
+// TLS site) even on platforms where the system certificate store is empty
+// or unavailable — most notably Android apps that ship without /etc/ssl/certs
+// and have no access to the OS cert store.
+//
+// Strategy:
+//  1. Try x509.SystemCertPool(). If it returns a non-empty pool, use it
+//     (this is the normal case on Linux/macOS/Windows desktops and servers).
+//  2. If SystemCertPool is unavailable or empty, fall back to the embedded
+//     Mozilla CA bundle (cacert.pem, the same one curl ships). This contains
+//     every CA in the Mozilla trust program, including HARICA TLS RSA/ECC
+//     Root CA 2021 which VK uses for *.vk.com since mid-2026.
+//  3. Also honor the SSL_CERT_FILE / SSL_CERT_DIR env vars if set, so users
+//     can override on unusual systems.
+//
+// Without this, on Android the tls-client (bogdanfinn) leaves RootCAs == nil,
+// which makes Go fall back to SystemCertPool — and on Android that pool is
+// empty, so every HTTPS request fails with:
+//
+//	tls: failed to verify certificate: x509: certificate signed by unknown authority
+//
+// See: https://github.com/cacggghp/vk-turn-proxy/issues/182 (and follow-ups).
+func loadCABundle() *x509.CertPool {
+	// 1. Honor explicit env overrides first (mirrors crypto/x509 behavior).
+	if file := os.Getenv("SSL_CERT_FILE"); file != "" {
+		if p, err := loadPoolFromFile(file); err == nil && p != nil {
+			log.Printf("[CABundle] using SSL_CERT_FILE=%s", file)
+			return p
+		}
+	}
+
+	// 2. Try the system pool.
+	if sys, err := x509.SystemCertPool(); err == nil && sys != nil && len(sys.Subjects()) > 0 {
+		log.Printf("[CABundle] using system cert pool (%d roots)", len(sys.Subjects()))
+		return sys
+	}
+
+	// 3. Fall back to the embedded Mozilla bundle.
+	pool := x509.NewCertPool()
+	if !pool.AppendCertsFromPEM(mozillaCABundlePEM) {
+		log.Printf("[CABundle] WARNING: embedded Mozilla bundle did not parse; HTTPS will likely fail")
+	} else {
+		log.Printf("[CABundle] using embedded Mozilla CA bundle (%d bytes)", len(mozillaCABundlePEM))
+	}
+	return pool
+}
+
+// loadPoolFromFile loads a PEM file with one or more certificates into a fresh
+// CertPool. Returns nil if the file contained no usable certificates.
+func loadPoolFromFile(path string) (*x509.CertPool, error) {
+	data, err := os.ReadFile(path)
+	if err != nil {
+		return nil, err
+	}
+	pool := x509.NewCertPool()
+	if !pool.AppendCertsFromPEM(data) {
+		return nil, nil
+	}
+	return pool, nil
+}
+
+// hasHTTPSInsecureEnv returns true if the user explicitly requested skipping
+// TLS verification (useful for debugging MITM proxies or stale CA bundles).
+// This is intentionally NOT exposed as a CLI flag — production should always
+// verify.
+func hasHTTPSInsecureEnv() bool {
+	v := strings.ToLower(os.Getenv("VKTURN_INSECURE_TLS"))
+	return v == "1" || v == "true" || v == "yes"
+}

client/captcha_parse_test.go

@@ -0,0 +1,146 @@
+package main
+
+import "testing"
+
+// TestParseVkCaptchaError_NewFormatWithoutCaptchaSid reproduces issue #182.
+//
+// VK started returning a captcha-required error (error_code 14) at the
+// calls.getAnonymousToken step in a NEW shape that only carries:
+//
+//	error_code, error_msg, is_enabled_captcha, redirect_uri
+//
+// and notably NO captcha_sid and NO captcha_img. The previous parser
+// rejected this payload with "missing captcha_sid in captcha error data"
+// and returned nil, so the auth loop never reached the captcha solver and
+// just fell through to the next client_id.
+//
+// After the fix, ParseVkCaptchaError must return a non-nil *VkCaptchaError
+// with RedirectURI + SessionToken populated so both the auto solver and the
+// manual (browser) solver can run.
+func TestParseVkCaptchaError_NewFormatWithoutCaptchaSid(t *testing.T) {
+	t.Parallel()
+
+	// Shape taken verbatim from the issue #182 log (session_token truncated
+	// for readability but structurally identical to the real payload).
+	errData := map[string]interface{}{
+		"error_code":         float64(14),
+		"error_msg":          "Captcha need",
+		"is_enabled_captcha": true,
+		"redirect_uri":       "https://id.vk.ru/not_robot_captcha?domain=vk.com&session_token=eyJhbGciOiJBMjU2R0NNS1ci.payload.signature&variant=popup&blank=1",
+		"captcha_stid":       "some-stid", // unrelated field, must be ignored
+	}
+
+	got := ParseVkCaptchaError(errData)
+	if got == nil {
+		t.Fatal("expected non-nil VkCaptchaError for new captcha format, got nil")
+	}
+
+	if got.ErrorCode != 14 {
+		t.Fatalf("ErrorCode = %d, want 14", got.ErrorCode)
+	}
+	if got.ErrorMsg != "Captcha need" {
+		t.Fatalf("ErrorMsg = %q, want %q", got.ErrorMsg, "Captcha need")
+	}
+	if got.RedirectURI == "" {
+		t.Fatal("RedirectURI is empty, expected the not_robot_captcha URL")
+	}
+	if got.SessionToken == "" {
+		t.Fatal("SessionToken is empty, expected it to be parsed from redirect_uri query")
+	}
+	if got.SessionToken != "eyJhbGciOiJBMjU2R0NNS1ci.payload.signature" {
+		t.Fatalf("SessionToken = %q, want the session_token query value", got.SessionToken)
+	}
+	// captcha_sid / captcha_img are absent in the new format and must default
+	// to empty strings (NOT cause the parser to bail out).
+	if got.CaptchaSid != "" {
+		t.Fatalf("CaptchaSid = %q, want empty (not present in new format)", got.CaptchaSid)
+	}
+	if got.CaptchaImg != "" {
+		t.Fatalf("CaptchaImg = %q, want empty (not present in new format)", got.CaptchaImg)
+	}
+
+	if !got.IsCaptchaError() {
+		t.Fatal("IsCaptchaError() = false, want true (new flow is solvable via redirect_uri + session_token)")
+	}
+}
+
+// TestParseVkCaptchaError_LegacyFormatStillWorks ensures the legacy captcha
+// payload (captcha_sid + captcha_img, no redirect_uri) still parses so the
+// manual HTTP captcha path keeps working.
+func TestParseVkCaptchaError_LegacyFormatStillWorks(t *testing.T) {
+	t.Parallel()
+
+	errData := map[string]interface{}{
+		"error_code":  float64(14),
+		"error_msg":   "Captcha need",
+		"captcha_sid": "1234567890",
+		"captcha_img": "https://api.vk.com/captcha.php?sid=1234567890&s=1",
+	}
+
+	got := ParseVkCaptchaError(errData)
+	if got == nil {
+		t.Fatal("expected non-nil VkCaptchaError for legacy captcha format, got nil")
+	}
+	if got.CaptchaSid != "1234567890" {
+		t.Fatalf("CaptchaSid = %q, want 1234567890", got.CaptchaSid)
+	}
+	if got.CaptchaImg == "" {
+		t.Fatal("CaptchaImg is empty, expected the captcha image URL")
+	}
+	if got.RedirectURI != "" {
+		t.Fatalf("RedirectURI = %q, want empty in legacy flow", got.RedirectURI)
+	}
+}
+
+// TestParseVkCaptchaError_NumericCaptchaSid covers the case where VK returns
+// captcha_sid as a JSON number (unmarshalled into float64).
+func TestParseVkCaptchaError_NumericCaptchaSid(t *testing.T) {
+	t.Parallel()
+
+	errData := map[string]interface{}{
+		"error_code":  float64(14),
+		"error_msg":   "Captcha need",
+		"captcha_sid": float64(9876543210),
+		"captcha_img": "https://api.vk.com/captcha.php?sid=9876543210",
+	}
+
+	got := ParseVkCaptchaError(errData)
+	if got == nil {
+		t.Fatal("expected non-nil VkCaptchaError, got nil")
+	}
+	if got.CaptchaSid != "9876543210" {
+		t.Fatalf("CaptchaSid = %q, want 9876543210", got.CaptchaSid)
+	}
+}
+
+// TestParseVkCaptchaError_UnsolvableReturnsNil verifies that when none of the
+// solvable fields are present, the parser returns nil so the caller surfaces
+// the raw VK error instead of pretending it can solve a captcha it cannot.
+func TestParseVkCaptchaError_UnsolvableReturnsNil(t *testing.T) {
+	t.Parallel()
+
+	errData := map[string]interface{}{
+		"error_code": float64(14),
+		"error_msg":  "Captcha need",
+		// no redirect_uri, no captcha_sid, no captcha_img
+	}
+
+	if got := ParseVkCaptchaError(errData); got != nil {
+		t.Fatalf("expected nil for unsolvable captcha payload, got %+v", got)
+	}
+}
+
+// TestParseVkCaptchaError_MissingErrorCodeReturnsNil verifies the parser still
+// rejects payloads that don't even identify as a VK API error object.
+func TestParseVkCaptchaError_MissingErrorCodeReturnsNil(t *testing.T) {
+	t.Parallel()
+
+	errData := map[string]interface{}{
+		"error_msg":    "Captcha need",
+		"redirect_uri": "https://id.vk.ru/not_robot_captcha?session_token=x",
+	}
+
+	if got := ParseVkCaptchaError(errData); got != nil {
+		t.Fatalf("expected nil when error_code is missing, got %+v", got)
+	}
+}

client/main.go

@@ -21,6 +21,7 @@ import (
 	neturl "net/url"
 	"os"
 	"os/signal"
+	"runtime"
 	"strconv"
 	"strings"
 	"sync"
@@ -67,6 +68,7 @@ var (
 	isDebug              bool
 	manualCaptcha        bool
 	autoCaptchaSliderPOC bool
+	captchaSolverURL     string // e.g. "http://127.0.0.1:8766" — Playwright-based solver
 )
 
 type captchaSolveMode int
@@ -75,9 +77,33 @@ const (
 	captchaSolveModeAuto captchaSolveMode = iota
 	captchaSolveModeSliderPOC
 	captchaSolveModeManual
+	captchaSolveModePlaywright
 )
 
 func captchaSolveModeForAttempt(attempt int, manualOnly bool, enableSliderPOC bool) (captchaSolveMode, bool) {
+	// If a Playwright solver URL is configured, try it FIRST — it's the only
+	// mode that reliably passes VK's bot detection (because the check request
+	// comes from a real Chromium with a real FingerprintJS visitor_id).
+	// Fall back to the legacy modes if the solver is unreachable / fails.
+	if captchaSolverURL != "" && !manualOnly {
+		switch attempt {
+		case 0:
+			return captchaSolveModePlaywright, true
+		case 1:
+			return captchaSolveModeAuto, true
+		case 2:
+			if enableSliderPOC {
+				return captchaSolveModeSliderPOC, true
+			}
+			return captchaSolveModeManual, true
+		case 3:
+			if enableSliderPOC {
+				return captchaSolveModeManual, true
+			}
+		}
+		return 0, false
+	}
+
 	if manualOnly {
 		return captchaSolveModeManual, attempt == 0
 	}
@@ -107,6 +133,8 @@ func captchaSolveModeLabel(mode captchaSolveMode) string {
 		return "auto captcha slider POC"
 	case captchaSolveModeManual:
 		return "manual captcha"
+	case captchaSolveModePlaywright:
+		return "playwright solver"
 	default:
 		return "captcha"
 	}
@@ -247,6 +275,53 @@ func generateFakeCursor() string {
 	return "[" + strings.Join(points, ",") + "]"
 }
 
+// generateConnectionRtt produces a realistic Navigator.connection.rtt sample
+// array. Real browsers observe slight per-sample variation around a baseline
+// (e.g. 50ms +/- 5-15ms jitter, occasional spikes). Sending the constant
+// [50,50,50,...] is a known bot fingerprint.
+func generateConnectionRtt(n int) string {
+	if n <= 0 {
+		n = 10
+	}
+	base := 45 + rand.Intn(40) // 45..84 ms baseline
+	parts := make([]string, 0, n)
+	for i := 0; i < n; i++ {
+		// jitter: -10..+30 ms, with occasional spike (+30..+90)
+		jitter := rand.Intn(41) - 10
+		if rand.Intn(8) == 0 { // ~12% chance of a spike
+			jitter += 30 + rand.Intn(60)
+		}
+		val := base + jitter
+		if val < 5 {
+			val = 5
+		}
+		parts = append(parts, strconv.Itoa(val))
+	}
+	return "[" + strings.Join(parts, ",") + "]"
+}
+
+// generateConnectionDownlink produces a realistic Navigator.connection.downlink
+// sample array. Real values are MBps floats with mild variation (e.g. 9.5, 9.6,
+// 9.4, 10.1, ...). Constant [9.5,9.5,...] is a known bot fingerprint.
+func generateConnectionDownlink(n int) string {
+	if n <= 0 {
+		n = 16
+	}
+	// baseline 5.0..15.0 Mbps, one decimal place
+	baseTenths := 50 + rand.Intn(100) // 5.0..14.9
+	parts := make([]string, 0, n)
+	for i := 0; i < n; i++ {
+		// jitter -3..+3 tenths
+		jitter := rand.Intn(7) - 3
+		t := baseTenths + jitter
+		if t < 10 {
+			t = 10 // floor at 1.0 Mbps
+		}
+		parts = append(parts, fmt.Sprintf("%.1f", float64(t)/10.0))
+	}
+	return "[" + strings.Join(parts, ",") + "]"
+}
+
 func getCustomNetDialer() net.Dialer {
 	return net.Dialer{
 		Timeout:   20 * time.Second,
@@ -287,7 +362,7 @@ type VkCaptchaError struct {
 }
 
 func ParseVkCaptchaError(errData map[string]interface{}) *VkCaptchaError {
-	// Extract error_code
+	// Extract error_code (required — identifies this as a VK API error object)
 	codeFloat, ok := errData["error_code"].(float64)
 	if !ok {
 		log.Printf("missing error_code in captcha error data")
@@ -295,48 +370,45 @@ func ParseVkCaptchaError(errData map[string]interface{}) *VkCaptchaError {
 	}
 	code := int(codeFloat)
 
-	// Extract redirect_uri
-	RedirectURI, ok := errData["redirect_uri"].(string)
-	if !ok {
-		log.Printf("missing redirect_uri in captcha error data")
-		return nil
-	}
+	// Extract redirect_uri (optional). Present in the NEW VK captcha flow where
+	// the user/automaton is redirected to https://id.vk.ru/not_robot_captcha?...
+	// Absent in the legacy captcha flow (which uses captcha_sid + captcha_img).
+	RedirectURI, _ := errData["redirect_uri"].(string)
 
-	// Extract captcha_sid
+	// Extract captcha_sid (optional in the new flow, required in the legacy flow).
 	captchaSid, ok := errData["captcha_sid"].(string)
 	if !ok {
 		// try numeric
 		if sidNum, ok2 := errData["captcha_sid"].(float64); ok2 {
 			captchaSid = fmt.Sprintf("%.0f", sidNum)
-		} else {
-			log.Printf("missing captcha_sid in captcha error data")
-			return nil
 		}
 	}
 
-	// Extract captcha_img
-	captchaImg, ok := errData["captcha_img"].(string)
-	if !ok {
-		log.Printf("missing captcha_img in captcha error data")
-		return nil
-	}
+	// Extract captcha_img (optional in the new flow, required in the legacy flow).
+	captchaImg, _ := errData["captcha_img"].(string)
 
-	// Extract error_msg
-	errorMsg, ok := errData["error_msg"].(string)
-	if !ok {
-		log.Printf("missing error_msg in captcha error data")
-		return nil
-	}
+	// Extract error_msg (optional — only used for logging/diagnostics).
+	errorMsg, _ := errData["error_msg"].(string)
 
 	// Extract session token if redirect_uri present
 	var sessionToken string
 	if RedirectURI != "" {
-		if parsed, err := neturl.Parse(RedirectURI); err == nil {
-			sessionToken = parsed.Query().Get("session_token")
-		} else {
+		parsed, err := neturl.Parse(RedirectURI)
+		if err != nil {
 			log.Printf("failed to parse redirect_uri: %v", err)
 			return nil
 		}
+		sessionToken = parsed.Query().Get("session_token")
+	}
+
+	// Require at least one solvable captcha path before returning a result:
+	//   - new flow:  redirect_uri + session_token (solved via not_robot_captcha)
+	//   - legacy flow: captcha_img (manual HTTP) typically paired with captcha_sid
+	// Without any of these, there is nothing the caller can do, so return nil
+	// and let the auth loop surface the raw VK API error.
+	if RedirectURI == "" && sessionToken == "" && captchaImg == "" && captchaSid == "" {
+		log.Printf("no solvable captcha path in error data: %v", errData)
+		return nil
 	}
 
 	// Extract is_sound_captcha_available
@@ -400,22 +472,26 @@ func solveVkCaptcha(ctx context.Context, captchaErr *VkCaptchaError, streamID in
 
 	log.Printf("[STREAM %d] [Captcha] PoW input: %s, difficulty: %d", streamID, bootstrap.PowInput, bootstrap.Difficulty)
 
-	hash := solvePoW(bootstrap.PowInput, bootstrap.Difficulty)
-	log.Printf("[STREAM %d] [Captcha] PoW solved: hash=%s", streamID, hash)
+	hexHash, nonce, ok := solvePoW(bootstrap.PowInput, bootstrap.Difficulty)
+	if !ok {
+		return "", fmt.Errorf("PoW solve exhausted nonce budget (input=%s, difficulty=%d)", bootstrap.PowInput, bootstrap.Difficulty)
+	}
+	powResult := formatPoWResult(hexHash, nonce)
+	log.Printf("[STREAM %d] [Captcha] PoW solved: hash=%s nonce=%d (v2-wrapped, len=%d)", streamID, hexHash, nonce, len(powResult))
 
 	var successToken string
 	if useSliderPOC {
 		successToken, err = callCaptchaNotRobotWithSliderPOC(
 			ctx,
 			captchaErr.SessionToken,
-			hash,
+			powResult,
 			streamID,
 			client,
 			profile,
 			bootstrap.Settings,
 		)
 	} else {
-		successToken, err = callCaptchaNotRobot(ctx, captchaErr.SessionToken, hash, streamID, client, profile)
+		successToken, err = callCaptchaNotRobot(ctx, captchaErr.SessionToken, powResult, streamID, client, profile)
 	}
 	if err != nil {
 		return "", fmt.Errorf("captchaNotRobot API failed: %w", err)
@@ -459,17 +535,64 @@ func fetchCaptchaBootstrap(ctx context.Context, redirectURI string, client tlscl
 	return parseCaptchaBootstrapHTML(string(body))
 }
 
-func solvePoW(powInput string, difficulty int) string {
+// solvePoW finds a nonce so that sha256(powInput + str(nonce)) starts with
+// `difficulty` zero characters. Returns (hexHash, nonce, ok).
+//
+// VK's not_robot_captcha.js stores the result as:
+//
+//	window.captchaPowResult = "v2." + btoa(JSON.stringify({ hash, nonce }))
+//
+// so callers must wrap the return value via formatPoWResult() before sending
+// it as the `hash` field of captchaNotRobot.check — sending the bare hex hash
+// is the #1 reason VK's bot detector flags the request as "BOT".
+func solvePoW(powInput string, difficulty int) (string, int, bool) {
 	target := strings.Repeat("0", difficulty)
 	for nonce := 1; nonce <= 10000000; nonce++ {
 		data := powInput + strconv.Itoa(nonce)
 		hash := sha256.Sum256([]byte(data))
 		hexHash := hex.EncodeToString(hash[:])
 		if strings.HasPrefix(hexHash, target) {
-			return hexHash
+			return hexHash, nonce, true
 		}
 	}
-	return ""
+	return "", 0, false
+}
+
+// formatPoWResult wraps (hash, nonce) into the v2.<base64(JSON)> format that
+// VK's not_robot_captcha.js produces. Mirrors:
+//
+//	"v2." + btoa(JSON.stringify({ hash, nonce }))
+//
+// where btoa is RFC 4648 standard base64 (no padding stripping).
+func formatPoWResult(hexHash string, nonce int) string {
+	payload := fmt.Sprintf(`{"hash":%q,"nonce":%d}`, hexHash, nonce)
+	encoded := base64.StdEncoding.EncodeToString([]byte(payload))
+	return "v2." + encoded
+}
+
+// captchaDebugInfoHardcoded is the fallback value VK's not_robot_captcha.js
+// sends when window.vk.brlefapmjnpg is undefined:
+//
+//	debug_info: window.vk?.brlefapmjnpg || "4045edac1cb2c18eff209dc09cd5e2e56475a13ed4615413a87618b3c6813f9a"
+//
+// Sending a random MD5 here (the previous behavior) is one of the strongest
+// bot signals VK checks.
+const captchaDebugInfoHardcoded = "4045edac1cb2c18eff209dc09cd5e2e56475a13ed4615413a87618b3c6813f9a"
+
+// formatCaptchaAnswer mirrors VK's not_robot_captcha.js:
+//
+//	answer: $w(JSON.stringify({ value: t }))
+//
+// where $w(s) = btoa(unescape(encodeURIComponent(s))) — i.e. standard base64
+// of the UTF-8 bytes. For a checkbox-style check, t is the user-event value;
+// passing an empty object matches what the JS sends for a synthetic click.
+func formatCaptchaAnswer(valueJSON string) string {
+	if valueJSON == "" {
+		valueJSON = "{}"
+	}
+	// JSON.stringify({value: t}) — t is already JSON-encoded by caller when needed
+	payload := `{"value":` + valueJSON + `}`
+	return base64.StdEncoding.EncodeToString([]byte(payload))
 }
 
 func callCaptchaNotRobot(ctx context.Context, sessionToken, hash string, streamID int, client tlsclient.HttpClient, profile Profile) (string, error) {
@@ -519,6 +642,21 @@ func callCaptchaNotRobot(ctx context.Context, sessionToken, hash string, streamI
 
 	baseParams := fmt.Sprintf("session_token=%s&domain=vk.com&adFp=&access_token=", neturl.QueryEscape(sessionToken))
 
+	// Step 0: initSession — VK's not_robot_captcha.js calls this before
+	// settings. Without it the server-side session state is not fully
+	// initialized, which is one of the signals that flags the request as
+	// "BOT" even when everything else looks legitimate.
+	log.Printf("[STREAM %d] [Captcha] Step 0/4: initSession", streamID)
+	if initResp, err := vkReq("captchaNotRobot.initSession", baseParams); err != nil {
+		log.Printf("[STREAM %d] [Captcha] Warning: initSession failed: %v (continuing)", streamID, err)
+	} else if respObj, ok := initResp["response"].(map[string]interface{}); ok {
+		if showType, _ := respObj["show_captcha_type"].(string); showType != "" {
+			log.Printf("[STREAM %d] [Captcha] initSession: show_captcha_type=%s", streamID, showType)
+		}
+	}
+
+	time.Sleep(200 * time.Millisecond)
+
 	log.Printf("[STREAM %d] [Captcha] Step 1/4: settings", streamID)
 	if _, err := vkReq("captchaNotRobot.settings", baseParams); err != nil {
 		return "", fmt.Errorf("settings failed: %w", err)
@@ -539,14 +677,19 @@ func callCaptchaNotRobot(ctx context.Context, sessionToken, hash string, streamI
 
 	log.Printf("[STREAM %d] [Captcha] Step 3/4: check", streamID)
 	cursorJSON := generateFakeCursor()
-	answer := base64.StdEncoding.EncodeToString([]byte("{}"))
+	// answer = $w(JSON.stringify({value: t})). For checkbox-style checks
+	// t is an empty object, so we wrap {} under "value".
+	answer := formatCaptchaAnswer("{}")
 
-	// Dynamically generate debug_info to avoid static fingerprint bans
-	debugInfoBytes := md5.Sum([]byte(profile.UserAgent + strconv.FormatInt(time.Now().UnixNano(), 10)))
-	debugInfo := hex.EncodeToString(debugInfoBytes[:])
+	// debug_info: VK's not_robot_captcha.js sends either window.vk.brlefapmjnpg
+	// (which we don't have, since we're not running inside the page) or the
+	// hardcoded fallback. Sending a random MD5 here is a strong bot signal.
+	debugInfo := captchaDebugInfoHardcoded
 
-	connectionRtt := "[50,50,50,50,50,50,50,50,50,50]"
-	connectionDownlink := "[9.5,9.5,9.5,9.5,9.5,9.5,9.5,9.5,9.5,9.5,9.5,9.5,9.5,9.5,9.5,9.5]"
+	// Realistic connection telemetry — slight per-sample jitter so the
+	// array doesn't look like a constant signature.
+	connectionRtt := generateConnectionRtt(10)
+	connectionDownlink := generateConnectionDownlink(16)
 
 	checkData := baseParams + fmt.Sprintf(
 		"&accelerometer=%s&gyroscope=%s&motion=%s&cursor=%s&taps=%s&connectionRtt=%s&connectionDownlink=%s&browser_fp=%s&hash=%s&answer=%s&debug_info=%s",
@@ -561,6 +704,16 @@ func callCaptchaNotRobot(ctx context.Context, sessionToken, hash string, streamI
 		return "", fmt.Errorf("check failed: %w", err)
 	}
 
+	// Log the raw check response so future debugging is easier. VK returns
+	// {status:"OK|BOT", success_token, show_captcha_type, redirect}.
+	if respObj, ok := checkResp["response"].(map[string]interface{}); ok {
+		status, _ := respObj["status"].(string)
+		showType, _ := respObj["show_captcha_type"].(string)
+		redirect, _ := respObj["redirect"].(string)
+		log.Printf("[STREAM %d] [Captcha] check response: status=%s show_captcha_type=%q redirect=%q",
+			streamID, status, showType, redirect)
+	}
+
 	respObj, ok := checkResp["response"].(map[string]interface{})
 	if !ok {
 		return "", fmt.Errorf("invalid check response: %v", checkResp)
@@ -816,12 +969,27 @@ func getTokenChain(ctx context.Context, link string, streamID int, creds VKCrede
 		SecChUaPlatform: `"Windows"`,
 	}
 
-	client, err := tlsclient.NewHttpClient(tlsclient.NewNoopLogger(),
+	clientOpts := []tlsclient.HttpClientOption{
 		tlsclient.WithTimeoutSeconds(20),
 		tlsclient.WithClientProfile(profiles.Chrome_146),
 		tlsclient.WithCookieJar(jar),
 		tlsclient.WithDialer(getCustomNetDialer()),
-	)
+	}
+	// Provide an explicit RootCAs pool. Without it, tls-client falls back
+	// to x509.SystemCertPool() which is empty on Android apps and causes
+	// every HTTPS request to fail with "x509: certificate signed by
+	// unknown authority". loadCABundle() handles system + embedded
+	// Mozilla fallback transparently.
+	if rootPool := loadCABundle(); rootPool != nil {
+		clientOpts = append(clientOpts, tlsclient.WithTransportOptions(
+			&tlsclient.TransportOptions{RootCAs: rootPool},
+		))
+	}
+	if hasHTTPSInsecureEnv() {
+		log.Printf("[STREAM %d] [VK Auth] WARNING: VKTURN_INSECURE_TLS set — skipping TLS verification (debug only!)", streamID)
+		clientOpts = append(clientOpts, tlsclient.WithInsecureSkipVerify())
+	}
+	client, err := tlsclient.NewHttpClient(tlsclient.NewNoopLogger(), clientOpts...)
 	if err != nil {
 		return "", "", "", fmt.Errorf("failed to initialize tls_client: %w", err)
 	}
@@ -936,6 +1104,16 @@ func getTokenChain(ctx context.Context, link string, streamID int, creds VKCrede
 				var solveErr error
 
 				switch solveMode {
+				case captchaSolveModePlaywright:
+					log.Printf("[STREAM %d] [Captcha] Using Playwright solver (real Chromium)...", streamID)
+					if captchaErr.RedirectURI != "" {
+						successToken, solveErr = solveCaptchaViaPlaywright(captchaErr.RedirectURI, streamID)
+						if solveErr != nil {
+							log.Printf("[STREAM %d] [Captcha] Playwright solver failed: %v", streamID, solveErr)
+						}
+					} else {
+						solveErr = fmt.Errorf("no redirect_uri for playwright solver")
+					}
 				case captchaSolveModeAuto:
 					if captchaErr.SessionToken != "" && captchaErr.RedirectURI != "" {
 						successToken, solveErr = solveVkCaptcha(ctx, captchaErr, streamID, client, profile, false)
@@ -1019,8 +1197,16 @@ func getTokenChain(ctx context.Context, link string, streamID int, creds VKCrede
 					data = fmt.Sprintf("vk_join_link=https://vk.com/call/join/%s&name=%s&captcha_key=%s&captcha_sid=%s&access_token=%s",
 						link, escapedName, neturl.QueryEscape(captchaKey), captchaErr.CaptchaSid, token1)
 				} else {
-					data = fmt.Sprintf("vk_join_link=https://vk.com/call/join/%s&name=%s&captcha_key=&captcha_sid=%s&is_sound_captcha=0&success_token=%s&captcha_ts=%s&captcha_attempt=%s&access_token=%s",
-						link, escapedName, captchaErr.CaptchaSid, neturl.QueryEscape(successToken), captchaErr.CaptchaTs, captchaErr.CaptchaAttempt, token1)
+					// New VK captcha flow: success_token was obtained from
+					// id.vk.ru/not_robot_captcha. captcha_sid is absent in this
+					// flow's error payload, so only include it when present to
+					// avoid sending an empty legacy field that could confuse VK.
+					sidPart := ""
+					if captchaErr.CaptchaSid != "" {
+						sidPart = "&captcha_sid=" + captchaErr.CaptchaSid
+					}
+					data = fmt.Sprintf("vk_join_link=https://vk.com/call/join/%s&name=%s&captcha_key=&is_sound_captcha=0&success_token=%s&captcha_ts=%s&captcha_attempt=%s%s&access_token=%s",
+						link, escapedName, neturl.QueryEscape(successToken), captchaErr.CaptchaTs, captchaErr.CaptchaAttempt, sidPart, token1)
 				}
 				continue
 			}
@@ -1784,6 +1970,13 @@ func oneTurnConnectionLoop(ctx context.Context, turnParams *turnParams, peer *ne
 }
 
 func main() {
+	// Build banner — printed as the very first line so users can confirm
+	// they are running the patched binary (issue #182 captcha fix + Android
+	// TLS/CA-bundle fix). If this line is missing from the log, an older
+	// binary is being launched by the wrapper/app.
+	log.Printf("vk-turn-proxy build: captcha-fix=v2 tls-ca-fix=v1 go=%s (issue#182 + HARICA root CA bundle embedded)",
+		runtime.Version())
+
 	ctx, cancel := context.WithCancel(context.Background())
 	globalAppCancel = cancel
 	defer cancel()
@@ -1812,6 +2005,7 @@ func main() {
 	vlessMode := flag.Bool("vless", false, "VLESS mode: forward TCP connections (for VLESS) instead of UDP packets")
 	debugFlag := flag.Bool("debug", false, "enable debug logging")
 	manualCaptchaFlag := flag.Bool("manual-captcha", false, "skip auto captcha solving, use manual mode immediately")
+	captchaSolverFlag := flag.String("captcha-solver", "", "URL of Playwright-based captcha solver (e.g. http://127.0.0.1:8766). When set, captcha is solved via real headless Chromium, bypassing VK's bot detection. Requires captcha_solver.py running on the host.")
 	flag.Parse()
 	if *peerAddr == "" {
 		log.Panicf("Need peer address!")
@@ -1827,6 +2021,10 @@ func main() {
 	isDebug = *debugFlag
 	manualCaptcha = *manualCaptchaFlag
 	autoCaptchaSliderPOC = !manualCaptcha
+	captchaSolverURL = *captchaSolverFlag
+	if captchaSolverURL != "" {
+		log.Printf("[Captcha] Playwright solver enabled: %s (will be tried first, then fallback to auto/manual)", captchaSolverURL)
+	}
 
 	var link string
 	var getCreds getCredsFunc

client/manual_captcha.go

@@ -615,3 +615,75 @@ func browserOpenCommands(goos string, url string) []browserCommand {
 	}
 	return nil
 }
+
+// solveCaptchaViaPlaywright delegates the captcha solving to an external
+// HTTP service (typically the captcha_solver.py Python script shipped in
+// /home/z/my-project/scripts/) that drives a real headless Chromium via
+// Playwright. The Chromium instance produces a real FingerprintJS visitor_id
+// and real behavioral telemetry, which is the only reliable way to pass
+// VK's not_robot_captcha bot detection.
+//
+// API contract:
+//
+//	POST <solverURL>/solve
+//	Body: {"redirect_uri": "https://id.vk.ru/not_robot_captcha?..."}
+//	Response: {"success_token": "...", "elapsed": 8.3}
+//	         or {"error": "...", "elapsed": 8.3}
+//
+// The solver must already be running (e.g. `python3 captcha_solver.py`).
+// Configure via `-captcha-solver http://127.0.0.1:8766` CLI flag.
+func solveCaptchaViaPlaywright(redirectURI string, streamID int) (string, error) {
+	if captchaSolverURL == "" {
+		return "", fmt.Errorf("no captcha solver URL configured")
+	}
+
+	payload := map[string]string{"redirect_uri": redirectURI}
+	body, err := json.Marshal(payload)
+	if err != nil {
+		return "", fmt.Errorf("marshal solver request: %w", err)
+	}
+
+	solveURL := strings.TrimRight(captchaSolverURL, "/") + "/solve"
+	log.Printf("[STREAM %d] [Captcha] Calling Playwright solver at %s", streamID, solveURL)
+
+	httpClient := &http.Client{Timeout: 60 * time.Second}
+	req, err := http.NewRequest("POST", solveURL, bytes.NewReader(body))
+	if err != nil {
+		return "", fmt.Errorf("build solver request: %w", err)
+	}
+	req.Header.Set("Content-Type", "application/json")
+
+	resp, err := httpClient.Do(req)
+	if err != nil {
+		return "", fmt.Errorf("solver HTTP call failed: %w", err)
+	}
+	defer func() { _ = resp.Body.Close() }()
+
+	respBody, err := io.ReadAll(resp.Body)
+	if err != nil {
+		return "", fmt.Errorf("read solver response: %w", err)
+	}
+
+	if resp.StatusCode != http.StatusOK {
+		return "", fmt.Errorf("solver returned HTTP %d: %s", resp.StatusCode, string(respBody))
+	}
+
+	var result struct {
+		SuccessToken string  `json:"success_token"`
+		Elapsed      float64 `json:"elapsed"`
+		Error        string  `json:"error"`
+	}
+	if err := json.Unmarshal(respBody, &result); err != nil {
+		return "", fmt.Errorf("parse solver response: %w (body: %s)", err, string(respBody))
+	}
+
+	if result.Error != "" {
+		return "", fmt.Errorf("solver error: %s", result.Error)
+	}
+	if result.SuccessToken == "" {
+		return "", fmt.Errorf("solver returned empty success_token")
+	}
+
+	log.Printf("[STREAM %d] [Captcha] Playwright solver returned success_token (elapsed=%.1fs)", streamID, result.Elapsed)
+	return result.SuccessToken, nil
+}

client/slider_captcha.go

@@ -23,7 +23,6 @@ import (
 )
 
 const (
-	captchaDebugInfo      = "1d3e9babfd3a74f4588bf90cf5c30d3e8e89a0e2a4544da8de8bbf4d78a32f5c"
 	sliderCaptchaType     = "slider"
 	defaultSliderAttempts = 4
 )
@@ -132,6 +131,23 @@ func (s *captchaNotRobotSession) requestSettings() (*captchaSettingsResponse, er
 	return parseCaptchaSettingsResponse(resp)
 }
 
+// requestInitSession mirrors VK's not_robot_captcha.js which calls
+// captchaNotRobot.initSession before settings. The response carries captcha_id
+// and content_settings (encrypted per-type config). Calling it sets up
+// server-side session state that the subsequent check expects.
+func (s *captchaNotRobotSession) requestInitSession() {
+	resp, err := s.request("captchaNotRobot.initSession", s.baseValues())
+	if err != nil {
+		log.Printf("[STREAM %d] [Captcha] Warning: initSession failed: %v (continuing)", s.streamID, err)
+		return
+	}
+	if respObj, ok := resp["response"].(map[string]interface{}); ok {
+		if showType, _ := respObj["show_captcha_type"].(string); showType != "" {
+			log.Printf("[STREAM %d] [Captcha] initSession: show_captcha_type=%s", s.streamID, showType)
+		}
+	}
+}
+
 func (s *captchaNotRobotSession) requestComponentDone() error {
 	values := s.baseValues()
 	values.Set("browser_fp", s.browserFp)
@@ -185,17 +201,31 @@ func (s *captchaNotRobotSession) requestCheck(cursor string, answer string) (*ca
 	values.Set("motion", "[]")
 	values.Set("cursor", cursor)
 	values.Set("taps", "[]")
-	values.Set("connectionRtt", "[]")
-	values.Set("connectionDownlink", "[]")
+	// Realistic connection telemetry with jitter (constant arrays are a bot fingerprint).
+	values.Set("connectionRtt", generateConnectionRtt(10))
+	values.Set("connectionDownlink", generateConnectionDownlink(16))
 	values.Set("browser_fp", s.browserFp)
 	values.Set("hash", s.hash)
 	values.Set("answer", answer)
-	values.Set("debug_info", captchaDebugInfo)
+	// VK's not_robot_captcha.js sends either window.vk.brlefapmjnpg or the
+	// hardcoded fallback. The previous captchaDebugInfo constant here was a
+	// different hardcoded MD5, which VK treats as a strong bot signal.
+	values.Set("debug_info", captchaDebugInfoHardcoded)
 
 	resp, err := s.request("captchaNotRobot.check", values)
 	if err != nil {
 		return nil, fmt.Errorf("check failed: %w", err)
 	}
+
+	// Log the raw check response so future debugging is easier.
+	if respObj, ok := resp["response"].(map[string]interface{}); ok {
+		status, _ := respObj["status"].(string)
+		showType, _ := respObj["show_captcha_type"].(string)
+		redirect, _ := respObj["redirect"].(string)
+		log.Printf("[STREAM %d] [Captcha] check response: status=%s show_captcha_type=%q redirect=%q",
+			s.streamID, status, showType, redirect)
+	}
+
 	return parseCaptchaCheckResult(resp)
 }
 
@@ -217,6 +247,10 @@ func callCaptchaNotRobotWithSliderPOC(
 ) (string, error) {
 	session := newCaptchaNotRobotSession(ctx, sessionToken, hash, streamID, client, profile)
 
+	log.Printf("[STREAM %d] [Captcha] Step 0/4: initSession", streamID)
+	session.requestInitSession()
+	time.Sleep(200 * time.Millisecond)
+
 	log.Printf("[STREAM %d] [Captcha] Step 1/4: settings", streamID)
 	settingsResp, err := session.requestSettings()
 	if err != nil {