pre-request.js

var getToken = true;

var client_id = pm.environment.get('CLIENT_ID');
var client_secret = pm.environment.get('CLIENT_SECRET');

if (!pm.environment.get('JWT_TOKEN')) {
    console.log('Token missing')
} else {
    
    var decoded = (pm.environment.get('JWT_TOKEN')).split('.')[1];
    var claims = JSON.parse(Buffer.from(decoded, 'base64'));

    var ts = Math.round((new Date()).getTime() / 1000);
  
    if (ts + 500 < claims.exp) {
        getToken = false;
    }
    
}

if (getToken === true) {
    console.log('Token expired missing')

    var params = {
        'scope': ['openid', 'name', 'groups', 'org', 'email'].join(' '),
        'client_id': client_id,
        'grant_type': 'urn:ietf:params:oauth:grant-type:jwt-bearer',
        'target': client_id,
        'api_type': 'app',
        'refresh_token': client_secret
    }

    const echoPostRequest = {
        url: 'https://accounts.descarteslabs.com/token',
        method: 'POST',
        header: 'Content-Type:application/json',
        body: {
            mode: 'application/json',
            raw: JSON.stringify(params)
        }
    };  

    var response = pm.sendRequest(echoPostRequest, function (err, res) {
        console.log(err ? err : res.json());
        if (err === null) {
            console.log('Saving the token')
            var responseJson = res.json();
            pm.environment.set('JWT_TOKEN', responseJson.id_token);
        }
    });

}