static base64ToArrayBuffer(base64) {
    const binaryString = atob(base64);
    const len = binaryString.length;
    const bytes = new Uint8Array(len);
    for (let i = 0; i < len; i++) {
      bytes[i] = binaryString.charCodeAt(i);
    }
    return bytes.buffer;
  }
Converts a base64 string to an ArrayBuffer
@param {string} base64
@returns {ArrayBuffer}