Add pre-request script for postman

pre-request-script.js

const stsEndpoint = pm.variables.get("STSEndpoint");
const clientCredentialBase64Encode = pm.variables.get("clientSecret64Encode");
const scopes = pm.variables.get("scopes");
let getToken = true;
const tokenEndpoint = stsEndpoint + '/connect/token';

if (!pm.variables.get('token')) {
    console.log('Token  missing');
} else {
    getToken = false;
    console.log('Token all good');
}

const echoPostRequest = {
    url: tokenEndpoint,
    method: 'POST',
    header: {
        'Authorization': clientCredentialBase64Encode,
        'Accept': 'application/json',
        'Content-Type': 'application/x-www-form-urlencoded',
    },
    body:{
        mode: 'urlencoded',
        urlencoded: [
            {key: "grant_type", value: "client_credentials", disabled: false},
            {key: "scope", value: scopes, disabled: false}
        ]
    }
};


if (getToken === true) {
    pm.sendRequest(echoPostRequest, function (err, res) {
        if (err === null) {
            var responseJson = res.json();
            pm.variables.set('token', responseJson.access_token);
        }
    });
}