public class ProdAuthentication {
  public static void main(String[] args) {
    HttpURLConnection connection = null;
    try {
      URL url = new URL("https://sts.itau.com.br/api/oauth/token");
      connection = (HttpURLConnection) url.openConnection();
      connection.addRequestProperty(
          "Content-Type", "application/x-www-form-urlencoded");
      connection.setRequestMethod("POST");
      connection.setDoOutput(true);

      // Add certificate
      File p12 = new File("{CAMINHO_CERTIFICADO}\\certificado.pfx");
      String p12password = "{SENHA_CERTIFICADO}";
      InputStream keyInput = new FileInputStream(p12);
      KeyStore keyStore = KeyStore.getInstance("PKCS12");
      keyStore.load(keyInput, p12password.toCharArray());
      keyInput.close();
      KeyManagerFactory keyManagerFactory =
          KeyManagerFactory.getInstance("SunX509");
      keyManagerFactory.init(keyStore, p12password.toCharArray());
      SSLContext context = SSLContext.getInstance("TLS");
      context.init(
          keyManagerFactory.getKeyManagers(), null, new SecureRandom());
      SSLSocketFactory socketFactory = context.getSocketFactory();
      if (connection instanceof HttpsURLConnection)
        ((HttpsURLConnection) connection).setSSLSocketFactory(socketFactory);
      //

      String body = "grant_type=client_credentials"
          + "&client_id={CLIENT_ID}"
          + "&client_secret={CLIENTE_SECRET}";
      OutputStream outputStream = connection.getOutputStream();
      outputStream.write(body.toString().getBytes());
      outputStream.close();
      BufferedReader bufferedReader = new BufferedReader(
          new InputStreamReader(connection.getInputStream()));
      StringBuilder response = new StringBuilder();
      String line = null;
      while ((line = bufferedReader.readLine()) != null) {
        response.append(line);
      }
      bufferedReader.close();
      System.out.println(response.toString());
    } catch (Exception e) {
      e.printStackTrace();
    } finally {
      if (connection != null)
        connection.disconnect();
    }
  }
}

import json
import requests

url = "https://sts.itau.com.br/api/oauth/token"
cert = ("./Certificado.crt", "./ARQUIVO_CHAVE_PRIVADA.key")
payload = 'grant_type=client_credentials&{CLEINT_ID}&client_secret={CLIENT_SECRET}'
headers = {
	'x-itau-flowID': "1",
	'x-itau-correlationID': "2",
	'Content-Type': 'application/x-www-form-urlencoded'
}

response = requests.post(url=url, data=payload, headers=headers, cert=cert)

if 200 != response.status_code:
	print(response.headers)

print(response.json())

<?php
$curl = curl_init();

$client_id = "{CLIENTE_ID}";
$client_secret = "{CLIENTE_SECRET}";

curl_setopt_array($curl, array(
    CURLOPT_URL => "https://api.itau.com.br/sandbox/api/oauth/token",
    CURLOPT_RETURNTRANSFER => true,
    CURLOPT_ENCODING => "",
    CURLOPT_MAXREDIRS => 10,
    CURLOPT_TIMEOUT => 0,
    CURLOPT_FOLLOWLOCATION => true,
    CURLOPT_HTTP_VERSION => CURL_HTTP_VERSION_1_1,
    CURLOPT_CUSTOMREQUEST => "POST",
    CURLOPT_SSLCERT => "CERTIFICAO.p12",
    CURLOPT_SSLCERTPASSWD => "PASSWORD",
    CURLOPT_SSLKEYTYPE => "P12",
    CURLOPT_POSTFIELDS => "grant_type=client_credentials&client_id=$client_id&client_secret=$client_secret",
    CURLOPT_HTTPHEADER => array(
		"Content-Type: application/x-www-form-urlencoded"
	),
));

$response = curl_exec($curl);

curl_close($curl);

echo $response;

public class ProdAuthentication
 {
  public string GetToKen(string ClientID, string ClientSecret) {
    HttpWebResponse requestResponse = null;
    var request = (HttpWebRequest) WebRequest.Create(
        "https://sts.itau.com.br/api/oauth/token");
    request.ContentType = "application/x-www-form-urlencoded";
    request.Method = "POST";
    var dataBody = "grant_type=" + Uri.EscapeDataString("client_credentials");
    dataBody += "&client_id=" + Uri.EscapeDataString(ClientID);
    dataBody += "&client_secret=" + Uri.EscapeDataString(ClientSecret);
    var body = Encoding.ASCII.GetBytes(dataBody);
    request.ContentLength = body.Length;
    string response = "";
    Stream myWriter = null;
    try {
      X509Certificate2 certificate = new X509Certificate2();
      certificate.Import(@"{CAMINHO_CERTIFICADO}\certificado.pfx",
          @"{SENHA_CERTIFICADO}", X509KeyStorageFlags.DefaultKeySet);
      request.ClientCertificates.Add(certificate);
      myWriter = request.GetRequestStream();
      myWriter.Write(body, 0, body.Length);
      requestResponse = (HttpWebResponse) request.GetResponse();
      response =
          new StreamReader(requestResponse.GetResponseStream()).ReadToEnd();
      return response;
    } catch (Exception ex) {
      var headerResponse = requestResponse.GetResponseHeader("");
      throw new Exception(
          "Erro ao solicitar o token.\r\nDetalhe: " + ex.Message);
    } finally {
      if (myWriter != null)
        myWriter.Close();
    }
  }
}