errore with messageSignature sha256 in postman (base64 is notdefined.) - postman

Question

I'm testing an api that i have to send in body those data acording to documentation:
studentId,
apiKey,
timeStamp (current iso time as a string),
messageSignature: apikey+studentId+timeStamp encrypted using sha256,
i wrote a script to generate message signature using sha256 in Pre-request Script.
Pre-request Script:
var dateIso = new Date().toISOString();
pm.globals.set("isoDateTostring", dateIso);
console.log('timestamp var is:', pm.globals.get("isoDateTostring"));
let msg = "apiKeyvalue" + "studentId" + pm.globals.get("isoDateTostring");+ JSON.stringify(msg)
const hmac = CryptoJS.algo.HMAC.create(CryptoJS.algo.SHA256, "secretKey");
hmac.update(msg);
const messageSignature = hmac.finalize().toString();
Details (like screenshots):
in body i wrote:
{
"studentId":"********",
"apiKey":"************",
"timeStamp":{{$isoDateTostring}},
"messageSignature": {{$messageSignature}}
}
when i send the request i get base64 is notdefined.

Answer 1

Code would be like:
In Tab Body:
{{$isoDateTostring}} --> "{{isoDateTostring}}"
{{$messageSignature}} --> "{{messageSignature}}"
{
"studentId": "123",
"apiKey": "123abc",
"timeStamp": "{{isoDateTostring}}",
"messageSignature": "{{messageSignature}}"
}
In tab Pre-request: I fake studentId and apiKey
const dateIso = new Date().toISOString();
pm.globals.set("isoDateTostring", dateIso);
const studentId = "123";
const apiKeyvalue = "123abc"
let msg = apiKeyvalue + studentId + pm.globals.get("isoDateTostring");
const messageSignature = CryptoJS.SHA256(msg).toString();
pm.globals.set("messageSignature", messageSignature);
Result:
{
"studentId": "123",
"apiKey": "123abc",
"timeStamp": "2021-10-26T13:20:09.068Z",
"messageSignature": "783e65ff1cfb2374fb5f84daa35c01d18b8a1898b3a1837e84934e91a3c0720d"
}