Postman pre-request script to fetch jwt tokens from cognito

prerequestscript.js

const echoPostRequest = {
    url: 'https://cognito-idp.us-west-2.amazonaws.com/',
    method: 'POST',
    header: {
          'Content-Type' : 'application/x-amz-json-1.1',
          'X-Amz-Target': 'AWSCognitoIdentityProviderService.InitiateAuth'
      },
    body: {
      mode: 'application/json',
      raw: JSON.stringify(
          {
              "AuthParameters" : {
                  "USERNAME" : pm.environment.get('credentialsUsername'),
                  "PASSWORD" : pm.environment.get('credentialsPassword')
          },
              "AuthFlow" : "USER_PASSWORD_AUTH",
              "ClientId" : pm.environment.get('cognitoPoolClientId')
      })
    }
  };
  
  var fetchTokenOnEveryRequest = pm.environment.get('fetchTokenOnEveryRequest') ? (pm.environment.get('fetchTokenOnEveryRequest')==='true'):false;
  
  var getToken = true;
  
  if(fetchTokenOnEveryRequest){
      console.log('removing previous token')
      pm.environment.unset('accessTokenExpiry')
  }
  if (!pm.environment.get('accessTokenExpiry') || 
      !pm.environment.get('currentAccessToken')) {
      console.log('Token or expiry date are missing')
  } else if (pm.environment.get('accessTokenExpiry') <= (new Date()).getTime()) {
      console.log('Token is expired')
  } else {
      getToken = false;
      console.log('Token and expiry date are all good');
  }
  
  
  if (getToken === true) {
      pm.sendRequest(echoPostRequest, function (err, res) {
      console.log(err ? err : res.json());
          if (err === null) {
              console.log('Saving the token and expiry date')
              var responseJson = res.json();
              console.log(responseJson.AuthenticationResult.ExpiresIn)
              pm.environment.set('currentAccessToken', responseJson.AuthenticationResult.IdToken)
              if(!fetchTokenOnEveryRequest){
                  var expiryDate = new Date();
                  expiryDate.setSeconds(expiryDate.getSeconds() + responseJson.AuthenticationResult.ExpiresIn);
                  pm.environment.set('accessTokenExpiry', expiryDate.getTime());
              }
          }
      });
  }