fire-entry-event-authentication.js

//authenticate to get access token
var authEndpoint = 'https://mcxxx.auth.marketingcloudapis.com/' //provide API endpoint
var payload = {
    client_id: "xxxxxx",    //pass Client ID
    client_secret: "xxxxxx",    //pass Client Secret
    grant_type: "client_credentials"
};
var url = authEndpoint + '/v2/token'
var contentType = 'application/json'

var accessTokenRequest = HTTP.Post(url, contentType, Stringify(payload));
if (accessTokenRequest.StatusCode == 200) {
   var tokenResponse = Platform.Function.ParseJSON(accessTokenRequest.Response[0]);
   var accessToken = tokenResponse.access_token
   var rest_instance_url = tokenResponse.rest_instance_url
};