code: async function prepareSignatures(signatures) {
    await Promise.all(signatures.map(async signature => {
      signature.signature = await signature.signature;
      try {
        signature.valid = await signature.verified;
      } catch(e) {
        signature.valid = null;
        signature.error = e;
        util.print_debug_error(e);
      }
    }));
  }
docs: Wait until signature objects have been verified
  @param  {Object} signatures              list of signatures