String apiUrl = "url";
    String wsUser = "YourWSUser";
    String wsPassword = "YourWSPassword";

    CredentialsProvider provider = new BasicCredentialsProvider();
    UsernamePasswordCredentials credentials = new UsernamePasswordCredentials(wsUser, wsPassword);
    provider.setCredentials(AuthScope.ANY, credentials);

    HttpClient client = HttpClientBuilder.create().setDefaultCredentialsProvider(provider).build();


    HttpPost httpRequest = new HttpPost(apiUrl);
    httpRequest.addHeader("Content-Type", "application/json");
    httpRequest.setEntity(new StringEntity(paymentRequest.toString(), "UTF-8"));
    HttpResponse httpResponse = client.execute(httpRequest);
    String paymentResponse = EntityUtils.toString(httpResponse.getEntity(), "UTF-8");

HttpRequest req = new HttpRequest();

    req.setEndpoint(apiUrl);
    req.setMethod('GET');

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

    req.setHeader('Content-Type', 'application/json');
    req.setBody(generator.getAsString());
    req.setTimeout(60000);


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