public class GetRestfulExample {
 private final String serviceEndpoint= 'https://devxxxx.service-now.com/api/now/table/incident.do';
public String Response { get; set;}
public String Headers { get; set; }

public void fetchData() {
    getAndParse('GET');
 }

public void getAndParse(String GET) {

// Get the XML document from the external server
Http http = new Http();
HttpRequest request = new HttpRequest();
String userName = 'xxx';
  String password = 'xxxx';

  // Specify the required user name and password to access the endpoint
  // As well as the header and header information
  Blob headerValue = Blob.valueOf(userName + ':' + password);
  String authorizationHeader = 'BASIC ' +
  EncodingUtil.base64Encode(headerValue);
request.setEndpoint(serviceEndpoint);

request.setMethod('GET');
  request.setHeader('Content-Type', 'application/json');
  // Header info with remote server user name and password
  request.setHeader('Authorization', authorizationHeader);
  // timeout in milliseconds
  request.setTimeout(120000);



  HttpResponse res = http.send(request);

System.debug(res.getBody());
 this.response=res.getBody();
 }
}

<apex:page controller="GetRestfulExample" action="{!fetchData}" contentType="text/plain">
 {!response}

setHeader('Accept','application/json');

HttpRequest req = new HttpRequest();
Http http = new Http();

Blob headerValue = Blob.valueOf(credentials.get('Username') + ':' + credentials.get('Password'));
String authorizationHeader = 'BASIC ' +
EncodingUtil.base64Encode(headerValue);
req.setHeader('Authorization', authorizationHeader);
req.setHeader('Content-Type', 'application/x-www-form-urlencoded');


req.setMethod('POST');
req.setBody(....);

String url = ....;

req.setEndPoint(url);

HTTPResponse resp = http.send(req);