export async function signMessage(message: string, secret: string): Promise<string> {
  const encoder = new TextEncoder();
  const key = await window.crypto.subtle.importKey(
    'raw',
    encoder.encode(secret),
    {name: 'HMAC', hash: {name: 'SHA-256'}},
    false,
    ['sign']
  );

  const signature = await window.crypto.subtle.sign('HMAC', key, encoder.encode(message));

  return Array.prototype.map.call(
    new Uint8Array(signature),
    (x: any) => ('00'+x.toString(16)).slice(-2)
  ).join('');
};