Http http = new Http();
HttpRequest request = new HttpRequest();
String reqUrl = 'https://api.abc.com/token';
request.setEndpoint(reqUrl);
request.setMethod('POST');
request.setHeader('Content-Type','application/x-www-form-urlencoded');
request.setHeader('Authorization','Basic T2dfT2Q2V1R3OHRkYUhyTkN6WlNwaVk0YldRYTpVW');
String payLoad = 'grant_type=password&username=test@ad.abc.com&password=O$Q3tz%Hdkqq&scope=PRODUCTION';
request.setBody(payLoad);
System.HttpResponse response = new System.Http().send(request);
system.debug(''+response.getBody());