async_usage.js

qz.security.setSignaturePromise(async (toSign) => {
    var pk = KEYUTIL.getKey(privateKey);
    var sig = new KJUR.crypto.Signature({"alg": "SHA1withRSA"});  // Use "SHA1withRSA" for QZ Tray 2.0 and older
    sig.init(pk); 
    sig.updateString(toSign);
    var hex = sig.sign();
    console.log("DEBUG: \n\n" + stob64(hextorstr(hex)));
    return stob64(hextorstr(hex));
});

qz.security.setCertificatePromise(async () => {
   return "-----BEGIN CERTIFICATE-----\n" +
       // ...
});

cert.js

/** Called to create new promise (using {@link _qz.security.certPromise}) for certificate retrieval. */
callCert: function() {
    if (typeof _qz.security.certPromise.then === 'function' || _qz.security.certPromise.constructor.name === "AsyncFunction") {
        return _qz.security.certPromise();
    } else {
        return _qz.tools.promise(_qz.security.certPromise);
    }
},

signature.js

/** Called to create new promise (using {@link _qz.security.signaturePromise}) for signed calls. */
callSign: function(toSign) {
    if (typeof _qz.security.signaturePromise.then === 'function' || _qz.security.signaturePromise.constructor.name === "AsyncFunction") {
        // Must be a promise, resolve toSign directly
        return _qz.security.signaturePromise(toSign);
    } else {
        // Standard function, wrap as a promise
        return _qz.tools.promise(_qz.security.signaturePromise(toSign));
    }
},