security: prevent websocket JWT leakage through URL query tokens (#349)

* security: prevent websocket JWT query authentication

* fix: harden websocket connection tickets

* fix: expire unused websocket tickets

src/utils/websocket-connection-token.ts

@@ -0,0 +1,86 @@
+import { generateUUID } from './uuid';
+
+const WEBSOCKET_NOTIFICATION_SCOPE = 'notifications.websocket';
+
+export interface WebSocketConnectionTokenClaims {
+  userId: string;
+  expiresAt: number;
+  nonce: string;
+  scope: typeof WEBSOCKET_NOTIFICATION_SCOPE;
+}
+
+function base64UrlEncode(data: Uint8Array): string {
+  return btoa(String.fromCharCode(...data))
+    .replace(/\+/g, '-')
+    .replace(/\//g, '_')
+    .replace(/=+$/, '');
+}
+
+function base64UrlDecode(value: string): Uint8Array {
+  let normalized = value.replace(/-/g, '+').replace(/_/g, '/');
+  while (normalized.length % 4) normalized += '=';
+  const binary = atob(normalized);
+  return Uint8Array.from(binary, (character) => character.charCodeAt(0));
+}
+
+async function getSigningKey(secret: string): Promise<CryptoKey> {
+  return crypto.subtle.importKey(
+    'raw',
+    new TextEncoder().encode(secret),
+    { name: 'HMAC', hash: 'SHA-256' },
+    false,
+    ['sign', 'verify']
+  );
+}
+
+export async function createWebSocketConnectionToken(
+  userId: string,
+  expiresAt: number,
+  secret: string
+): Promise<string> {
+  const claims: WebSocketConnectionTokenClaims = {
+    userId,
+    expiresAt,
+    nonce: generateUUID(),
+    scope: WEBSOCKET_NOTIFICATION_SCOPE,
+  };
+  const payload = base64UrlEncode(new TextEncoder().encode(JSON.stringify(claims)));
+  const signature = await crypto.subtle.sign(
+    'HMAC',
+    await getSigningKey(secret),
+    new TextEncoder().encode(payload)
+  );
+  return `${payload}.${base64UrlEncode(new Uint8Array(signature))}`;
+}
+
+export async function verifyWebSocketConnectionToken(
+  token: string,
+  secret: string
+): Promise<WebSocketConnectionTokenClaims | null> {
+  try {
+    if (!token || token.length > 1024) return null;
+    const parts = token.split('.');
+    if (parts.length !== 2) return null;
+    const [payload, encodedSignature] = parts;
+    const valid = await crypto.subtle.verify(
+      'HMAC',
+      await getSigningKey(secret),
+      base64UrlDecode(encodedSignature),
+      new TextEncoder().encode(payload)
+    );
+    if (!valid) return null;
+
+    const claims = JSON.parse(new TextDecoder().decode(base64UrlDecode(payload))) as Partial<WebSocketConnectionTokenClaims>;
+    if (
+      claims.scope !== WEBSOCKET_NOTIFICATION_SCOPE
+      || !String(claims.userId || '').trim()
+      || !Number.isFinite(claims.expiresAt)
+      || Number(claims.expiresAt) <= Date.now()
+    ) {
+      return null;
+    }
+    return claims as WebSocketConnectionTokenClaims;
+  } catch {
+    return null;
+  }
+}