postman_oauth_test.js

let userSecret = "your_user_secret";
let clientSecret = "your_client_secret";
let host_url = 'your_host_url';
let scope = 'your_app_scope';

let toEncode = userSecret +":"+ clientSecret;
toEncode = btoa(toEncode);
pm.environment.set("auth_token", toEncode);
pm.environment.set("host_url", host_url);

pm.environment.set("accessToken", "");

//edit URL to be the one of the token generator
const echoPostRequest = {
    url: 'https://'+host_url+'/oauther/oauth2/token',
    method: 'POST',
    header: {
        'Content-Type':'application/x-www-form-urlencoded',
        'Host': host_url,
        'Authorization' : 'Basic ' + toEncode
    },
    body: {
    mode: 'raw',
    raw: 'grant_type=client_credentials&scope=' + scope
    }
};

pm.sendRequest(echoPostRequest, function (err, response) {
    console.log(response.json());
    let respJson = response.json();
    if(respJson.access_token) {
        let access_token = respJson.access_token;
        pm.environment.set('accessToken', access_token);
        pm.test("Access token available and saved.")
    } else {
        pm.test("Pre-script failure", function() {
            throw new Error("Access token missing from response.");
        })
    }
});