DirectCallOut

HttpRequest req = new HttpRequest();
req.setEndpoint('https://my_endpoint.example.com/some_path');
req.setMethod('GET');

// Because we didn't set the endpoint as a named credential,
// our code has to specify:
// - The required username and password to access the endpoint
// - The header and header information

String username = 'myname';
String password = 'mypwd';  
Blob headerValue = Blob.valueOf(username + ':' + password);
String authorizationHeader = 'BASIC ' +
EncodingUtil.base64Encode(headerValue);
req.setHeader('Authorization', authorizationHeader);

// Create a new http object to send the request object
// A response object is generated as a result of the request  

Http http = new Http();
HTTPResponse res = http.send(req);
System.debug(res.getBody());