diff --git a/src/Auth.php b/src/Auth.php
index f7db881..5291ea0 100644
--- a/src/Auth.php
+++ b/src/Auth.php
@@ -129,7 +129,45 @@ final class Auth {
     }
 
     public static function clearPending2fa(): void {
-        unset($_SESSION['pending_2fa_user_id'], $_SESSION['pending_2fa_exp']);
+        unset($_SESSION['pending_2fa_user_id'], $_SESSION['pending_2fa_exp'], $_SESSION['pending_2fa_approval_token']);
+    }
+
+    /**
+     * Complete login via a cross-device approval token (no TOTP code required).
+     * The approval token must have been approved by the authenticated mobile user.
+     */
+    public static function completeTotpLoginByApproval(string $rawToken): bool {
+        $uid = self::pending2faUserId();
+        if ($uid <= 0) {
+            return false;
+        }
+        $sessionId = session_id();
+        $consumedUid = AuthApproval::consume($rawToken, $sessionId);
+        if ($consumedUid <= 0 || $consumedUid !== $uid) {
+            return false;
+        }
+        self::clearPending2fa();
+        $stmt = Database::pdo()->prepare('SELECT * FROM users WHERE id = ? LIMIT 1');
+        $stmt->execute([$consumedUid]);
+        $row = $stmt->fetch();
+        if (!$row) {
+            return false;
+        }
+        $_SESSION['user'] = Rbac::buildSessionUser($row);
+        return true;
+    }
+
+    /** Best-effort client IP (respects X-Forwarded-For from trusted proxy). */
+    public static function clientIp(): string {
+        $fwd = (string) ($_SERVER['HTTP_X_FORWARDED_FOR'] ?? '');
+        if ($fwd !== '') {
+            // Take the first (original client) IP from the chain
+            $first = trim(explode(',', $fwd)[0]);
+            if (filter_var($first, FILTER_VALIDATE_IP)) {
+                return $first;
+            }
+        }
+        return (string) ($_SERVER['REMOTE_ADDR'] ?? '0.0.0.0');
     }
 
     public static function logout(): void {
diff --git a/src/AuthApproval.php b/src/AuthApproval.php
new file mode 100644
index 0000000..5fd041e
--- /dev/null
+++ b/src/AuthApproval.php
@@ -0,0 +1,150 @@
+<?php
+declare(strict_types=1);
+
+/**
+ * Cross-device 2FA approval tokens.
+ *
+ * Flow:
+ *   1. Desktop reaches /two-factor: AuthApproval::create() mints a token,
+ *      stores it with the desktop session ID and pending user ID.
+ *   2. QR code encodes: <appRoot>/two-factor/approve?token=<raw_token>
+ *   3. Mobile (already logged in) opens that URL, sees a confirm page,
+ *      POSTs to /two-factor/approve → AuthApproval::approve() sets status=approved.
+ *   4. Desktop polls /api/two-factor/poll?token=<raw_token> every ~2.5 s.
+ *      When status=approved, Auth::completeTotpLoginByApproval() is called,
+ *      which validates the approval and completes the session.
+ *
+ * IP hashes are SHA-256(IP) — anonymous geolocation audit trail.
+ */
+final class AuthApproval {
+    private const TTL_SECONDS = 300;
+
+    private function __construct() {
+    }
+
+    /** Mint a new approval token tied to the current desktop session and pending user. */
+    public static function create(int $userId, string $desktopSessionId, string $requesterIp): string {
+        AuthEmailSchema::ensure(Database::pdo());
+        $rawToken = bin2hex(random_bytes(32));
+        $tokenHash = hash('sha256', $rawToken);
+        $ipHash = hash('sha256', $requesterIp);
+        $expiresAt = date('Y-m-d H:i:s', time() + self::TTL_SECONDS);
+        $pdo = Database::pdo();
+        // Clean up expired tokens for this session first
+        $pdo->prepare(
+            "DELETE FROM auth_approvals WHERE desktop_session_id = ? AND expires_at < NOW()"
+        )->execute([$desktopSessionId]);
+        $pdo->prepare(
+            "INSERT INTO auth_approvals
+                (token_hash, desktop_session_id, user_id, status, requester_ip_hash, expires_at)
+             VALUES (?, ?, ?, 'pending', ?, ?)"
+        )->execute([$tokenHash, $desktopSessionId, $userId, $ipHash, $expiresAt]);
+        return $rawToken;
+    }
+
+    /**
+     * Approve a token (called by the mobile user on POST /two-factor/approve).
+     * Returns true on success, false if token not found / expired / wrong user.
+     */
+    public static function approve(string $rawToken, int $approvingUserId, string $approverIp): bool {
+        $tokenHash = hash('sha256', $rawToken);
+        $ipHash = hash('sha256', $approverIp);
+        $pdo = Database::pdo();
+        $st = $pdo->prepare(
+            "SELECT id, user_id, status, expires_at FROM auth_approvals WHERE token_hash = ? LIMIT 1"
+        );
+        $st->execute([$tokenHash]);
+        $row = $st->fetch();
+        if (!$row) {
+            return false;
+        }
+        if ($row['status'] !== 'pending') {
+            return false;
+        }
+        if (strtotime((string) $row['expires_at']) < time()) {
+            $pdo->prepare("UPDATE auth_approvals SET status='expired' WHERE id=?")->execute([$row['id']]);
+            return false;
+        }
+        // The approving user must be the same user waiting on desktop
+        if ((int) $row['user_id'] !== $approvingUserId) {
+            return false;
+        }
+        $pdo->prepare(
+            "UPDATE auth_approvals SET status='approved', approver_ip_hash=?, approved_at=NOW() WHERE id=?"
+        )->execute([$ipHash, $row['id']]);
+        return true;
+    }
+
+    /**
+     * Poll status for a raw token.
+     * Returns 'pending'|'approved'|'expired'|'used'|'not_found'.
+     * Also marks expired rows in the DB.
+     */
+    public static function pollStatus(string $rawToken): string {
+        $tokenHash = hash('sha256', $rawToken);
+        $pdo = Database::pdo();
+        $st = $pdo->prepare(
+            "SELECT id, status, expires_at, user_id, desktop_session_id
+             FROM auth_approvals WHERE token_hash = ? LIMIT 1"
+        );
+        $st->execute([$tokenHash]);
+        $row = $st->fetch();
+        if (!$row) {
+            return 'not_found';
+        }
+        if ($row['status'] === 'pending' && strtotime((string) $row['expires_at']) < time()) {
+            $pdo->prepare("UPDATE auth_approvals SET status='expired' WHERE id=?")->execute([$row['id']]);
+            return 'expired';
+        }
+        return (string) $row['status'];
+    }
+
+    /**
+     * Consume an approved token and return the user_id.
+     * Returns 0 if the token is not in 'approved' state or doesn't match the session.
+     */
+    public static function consume(string $rawToken, string $desktopSessionId): int {
+        $tokenHash = hash('sha256', $rawToken);
+        $pdo = Database::pdo();
+        $st = $pdo->prepare(
+            "SELECT id, user_id, status, desktop_session_id, expires_at
+             FROM auth_approvals WHERE token_hash = ? LIMIT 1"
+        );
+        $st->execute([$tokenHash]);
+        $row = $st->fetch();
+        if (!$row) {
+            return 0;
+        }
+        if ($row['status'] !== 'approved') {
+            return 0;
+        }
+        if ($row['desktop_session_id'] !== $desktopSessionId) {
+            return 0;
+        }
+        if (strtotime((string) $row['expires_at']) < time()) {
+            return 0;
+        }
+        $pdo->prepare(
+            "UPDATE auth_approvals SET status='used', used_at=NOW() WHERE id=?"
+        )->execute([$row['id']]);
+        return (int) $row['user_id'];
+    }
+
+    /** Lookup the user_id and desktop_session_id for a token (for the approve confirmation page). */
+    public static function getForToken(string $rawToken): ?array {
+        $tokenHash = hash('sha256', $rawToken);
+        $st = Database::pdo()->prepare(
+            "SELECT user_id, desktop_session_id, status, expires_at
+             FROM auth_approvals WHERE token_hash = ? LIMIT 1"
+        );
+        $st->execute([$tokenHash]);
+        $row = $st->fetch();
+        if (!$row) {
+            return null;
+        }
+        if ($row['status'] !== 'pending' || strtotime((string) $row['expires_at']) < time()) {
+            return null;
+        }
+        return $row;
+    }
+}
diff --git a/src/AuthEmailSchema.php b/src/AuthEmailSchema.php
index c952253..1e5c2a5 100644
--- a/src/AuthEmailSchema.php
+++ b/src/AuthEmailSchema.php
@@ -21,6 +21,7 @@ final class AuthEmailSchema {
             self::ensureAuthTokens($pdo);
             self::ensureAuthFactors($pdo);
             self::ensureAuthAttempts($pdo);
+            self::ensureAuthApprovals($pdo);
         });
         self::$ensured = true;
     }
@@ -136,5 +137,48 @@ final class AuthEmailSchema {
                 created_at TEXT NOT NULL DEFAULT (datetime('now'))
             )"
         );
+        $pdo->exec('CREATE INDEX IF NOT EXISTS idx_auth_attempts_ip ON auth_attempts (ip_hash, created_at)');
+    }
+
+    private static function ensureAuthApprovals(PDO $pdo): void {
+        if (Database::tableExists($pdo, 'auth_approvals')) {
+            return;
+        }
+        if (Database::isMysql()) {
+            $pdo->exec(
+                "CREATE TABLE auth_approvals (
+                    id BIGINT UNSIGNED AUTO_INCREMENT PRIMARY KEY,
+                    token_hash CHAR(64) NOT NULL UNIQUE,
+                    desktop_session_id VARCHAR(128) NOT NULL,
+                    user_id INT UNSIGNED NOT NULL,
+                    status ENUM('pending','approved','used','expired') NOT NULL DEFAULT 'pending',
+                    requester_ip_hash CHAR(64) NULL,
+                    approver_ip_hash CHAR(64) NULL,
+                    expires_at TIMESTAMP NOT NULL,
+                    approved_at TIMESTAMP NULL,
+                    used_at TIMESTAMP NULL,
+                    created_at TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP,
+                    KEY idx_auth_approvals_token (token_hash),
+                    KEY idx_auth_approvals_session (desktop_session_id)
+                ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci"
+            );
+            return;
+        }
+        $pdo->exec(
+            "CREATE TABLE auth_approvals (
+                id INTEGER PRIMARY KEY AUTOINCREMENT,
+                token_hash TEXT NOT NULL UNIQUE,
+                desktop_session_id TEXT NOT NULL,
+                user_id INTEGER NOT NULL,
+                status TEXT NOT NULL DEFAULT 'pending',
+                requester_ip_hash TEXT NULL,
+                approver_ip_hash TEXT NULL,
+                expires_at TEXT NOT NULL,
+                approved_at TEXT NULL,
+                used_at TEXT NULL,
+                created_at TEXT NOT NULL DEFAULT (datetime('now'))
+            )"
+        );
+        $pdo->exec('CREATE UNIQUE INDEX IF NOT EXISTS idx_auth_approvals_token ON auth_approvals (token_hash)');
     }
 }
diff --git a/src/AuthTwoFactorPage.php b/src/AuthTwoFactorPage.php
index 31ecbd6..05ac044 100644
--- a/src/AuthTwoFactorPage.php
+++ b/src/AuthTwoFactorPage.php
@@ -1,35 +1,56 @@
 <?php
 declare(strict_types=1);
 
-/** 2FA challenge page helpers (QR short link for mobile handoff). */
+/** 2FA challenge page helpers — cross-device approval QR. */
 final class AuthTwoFactorPage {
-    /** @return array{short_url?:string,qr_url?:string,long_url:string}|null */
+    /**
+     * Build the QR payload for the 2FA challenge screen.
+     *
+     * Returns an array with:
+     *   long_url    – approval URL (fallback if shortener unavailable)
+     *   short_url   – shortened URL (s.f0xx.org)
+     *   qr_url      – URL of the QR PNG image (short_url + ?src=qr)
+     *   raw_token   – the approval token to store in session for polling
+     *
+     * @return array{long_url:string,short_url?:string,qr_url?:string,raw_token:string}|null
+     */
     public static function qrPayload(): ?array {
         $uid = Auth::pending2faUserId();
         if ($uid <= 0) {
             return null;
         }
         $project = Auth::projectBasePath();
-        $longUrl = 'https://apps.f0xx.org' . $project . '/?ref=2fa&uid=' . $uid;
+        $ip = Auth::clientIp();
+        $rawToken = AuthApproval::create($uid, session_id(), $ip);
+
+        // Store token in session so the poll endpoint can reference it
+        $_SESSION['pending_2fa_approval_token'] = $rawToken;
+
+        $approveUrl = 'https://apps.f0xx.org' . $project . '/two-factor/approve?token=' . urlencode($rawToken);
+
         if (!UrlShortenerDatabase::enabled() || !UrlShortenerDatabase::ping()) {
-            return ['long_url' => $longUrl];
+            return ['long_url' => $approveUrl, 'raw_token' => $rawToken];
         }
         $bearers = ShortLinksRepository::listBearers();
         if ($bearers === []) {
-            return ['long_url' => $longUrl];
+            return ['long_url' => $approveUrl, 'raw_token' => $rawToken];
         }
         $bearerId = (int) ($bearers[0]['id'] ?? 0);
         if ($bearerId <= 0) {
-            return ['long_url' => $longUrl];
+            return ['long_url' => $approveUrl, 'raw_token' => $rawToken];
         }
-        $mint = ShortLinksRepository::createLink($bearerId, $longUrl, 900);
+        $mint = ShortLinksRepository::createLink($bearerId, $approveUrl, 900);
         if (empty($mint['ok'])) {
-            return ['long_url' => $longUrl];
+            return ['long_url' => $approveUrl, 'raw_token' => $rawToken];
         }
+        $shortUrl = (string) ($mint['short_url'] ?? '');
+        // QR image encodes the short URL with ?src=qr so mobile scans are tracked
+        $qrUrl = $shortUrl . (str_contains($shortUrl, '?') ? '&src=qr' : '?src=qr');
         return [
-            'long_url' => $longUrl,
-            'short_url' => (string) ($mint['short_url'] ?? ''),
-            'qr_url' => (string) ($mint['qr_url'] ?? ''),
+            'long_url'  => $approveUrl,
+            'short_url' => $shortUrl,
+            'qr_url'    => $qrUrl,
+            'raw_token' => $rawToken,
         ];
     }
 }