A postman pre-request script to fetch a valid token from Red Hat SSO (Keycloak) and set it to a template variable to use in request headers.

keycloak-fetch-token-postman-pre-request.js

// modify these configurations to work with your environment
var server = "https://sso.example.com";
var realm = "realm";
var resource = "client";
var username = "username";
var password = "url encoded password";

var url = `${server}/auth/realms/${realm}/protocol/openid-connect/token`;
var data = `grant_type=password&client_id=${resource}&username=${username}&password=${password}`;

var xhr = new XMLHttpRequest();
xhr.withCredentials = true;

xhr.addEventListener("readystatechange", function () {
  if (this.readyState === 4) {
    // set a global variable if we are not using environemnts
    postman.setGlobalVariable('token', JSON.parse(this.responseText).access_token);
    // use this if working within an environment
    // postman.setEnvironmentVariable('token', JSON.parse(this.responseText).access_token);
  }
});

xhr.open("POST", url);
xhr.setRequestHeader("content-type", "application/x-www-form-urlencoded");
xhr.send(data);