Pre request script for the Post request

post-Prerequest.js

// Sketchy loading of the jsrsasign library into Postman Sandbox
var navigator = {}; //fake a navigator object for the lib
var window = {}; //fake a window object for the lib
eval(pm.globals.get("jsrsasign-js")); //import javascript jsrsasign

var currentTime = +new Date(); // the current time in milliseconds
var issuedAtTimeSeconds = currentTime/1000;
var expirationTimeSeconds = currentTime/1000 + 2592000;



// Generate random string for "jti" claim - needed if client has Replay Prevention enabled
var newJti="";
var charset = "abcdefghijklmnopqrstuvwxyz0123456789";

for( var i=0; i < 12; i++ ) {
    newJti += charset.charAt(Math.floor(Math.random() * charset.length));
}

pm.variables.set("jti", newJti);

// Create Header and Payload objects
var header = {
    "typ": "JWT",
  "kid": "DwMKdWMmj7PWinvoqfQyXVzyZ6Q",
  "alg": "PS256"
};

var payload = {
  "iss": "9b5usDpbNtmxDcTzs7GzKp",
  "exp" : Math.ceil(expirationTimeSeconds),
  "iat" : Math.ceil(issuedAtTimeSeconds),
  "jti": "1601982046",
  "aud": "https://localhost:8243/token",
  "scope": "accounts payments",
  "token_endpoint_auth_method": "private_key_jwt",
  "grant_types": [
    "authorization_code",
    "refresh_token"
  ],
  "response_types": [
    "code id_token"
  ],
  "id_token_signed_response_alg": "PS256",
  "request_object_signing_alg": "PS256",
  "software_id": "9b5usDpbNtmxDcTzs7GzKp",
  "application_type": "web",
  "redirect_uris": [
    "https://wso2.com"
  ],
  "token_endpoint_auth_signing_alg": "PS256",
  "software_statement": pm.environment.get("software_statement"),
  "backchannel_token_delivery_mode": "ping",
  "backchannel_client_notification_endpoint": "https://docs.wso2.com/display/OB200/Dynamic+Client+Registration+v3.2#c97c86b28d9d4688992e0eab0bd4bf1b",
  "backchannel_authentication_request_signing_alg": "PS256",
  "backchannel_user_code_parameter_supported": false
};

// Prep the objects for a JWT
var sHeader = JSON.stringify(header);
var sPayload = JSON.stringify(payload);

var prvKey = pm.globals.get("private_key");

var sJWT = KJUR.jws.JWS.sign(header.alg, sHeader, sPayload, prvKey);

pm.environment.set("post_body", sJWT);