feat(streams): add on-demand live request accept end and playback token APIs

Backend/utils/stream-token.ts

@@ -0,0 +1,31 @@
+import { createHmac } from 'crypto';
+
+type StreamPlaybackPayload = {
+  sessionId: string;
+  viewerDeviceId: string;
+  userId: string;
+  exp: number;
+};
+
+const secret = process.env.BETTER_AUTH_SECRET;
+
+if (!secret) {
+  throw new Error('BETTER_AUTH_SECRET is required for stream playback token signing');
+}
+
+const sign = (data: string): string => createHmac('sha256', secret).update(data).digest('base64url');
+
+export const createStreamPlaybackToken = (
+  payload: Omit<StreamPlaybackPayload, 'exp'>,
+  ttlSeconds = 60 * 15,
+): string => {
+  const body: StreamPlaybackPayload = {
+    ...payload,
+    exp: Math.floor(Date.now() / 1000) + ttlSeconds,
+  };
+
+  const encodedPayload = Buffer.from(JSON.stringify(body), 'utf8').toString('base64url');
+  const signature = sign(encodedPayload);
+
+  return `${encodedPayload}.${signature}`;
+};