android { //...  compileOptions { targetCompatibility = "8" sourceCompatibility = "8" } } dependencies { //... implementation 'com.squareup.okhttp3:okhttp:3.14.1' } 

 <manifest> //... <uses-permission android:name="android.permission.INTERNET" /> <application android:usesCleartextTraffic="true"> /... </application> </manifest> 

<?xml version="1.0" encoding="utf-8"?> <network-security-config> <domain-config cleartextTrafficPermitted="true"> <domain includeSubdomains="true">127.0.0.1</domain> </domain-config> </network-security-config> 

 import java.io.IOException; import okhttp3.Credentials; import okhttp3.Interceptor; import okhttp3.Request; import okhttp3.Response; public class BasicAuthInterceptor implements Interceptor { private String credentials; public BasicAuthInterceptor(String user, String password) { this.credentials = Credentials.basic(user, password); } @Override public Response intercept(Chain chain) throws IOException { Request request = chain.request(); Request authenticatedRequest = request.newBuilder() .header("Authorization", credentials).build(); return chain.proceed(authenticatedRequest); } } 

 import java.io.IOException; import okhttp3.Call; import okhttp3.Callback; import okhttp3.MediaType; import okhttp3.OkHttpClient; import okhttp3.Request; import okhttp3.RequestBody; import okhttp3.Response; public class MainActivity extends AppCompatActivity { public OkHttpClient client; public static final MediaType CONTENT_TYPE = MediaType.get("application/x-www-form-urlencoded"); String apUrl = "www.example.com/oauth/token"; // replace host url through your oauth2 server. @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); client = new OkHttpClient.Builder() .addInterceptor(new BasicAuthInterceptor("USER_CLIENT_APP", "password")) .build(); String username = "user"; String password = "password"; String grant_type = "password"; String requestData = "grant_type=" + grant_type + "&username=" + username + "&password=" + password; try { loginRequest(apUrl, requestData); } catch (IOException e) { e.printStackTrace(); } } public void loginRequest(String apUrl, String requestData) throws IOException { RequestBody body = RequestBody.create(CONTENT_TYPE, requestData); Request request = new Request.Builder() .url(apUrl) .addHeader("Content-Type", " application/x-www-form-urlencoded") .post(body) .build(); Call call = client.newCall(request); call.enqueue(new Callback() { @Override public void onFailure(Call call, IOException e) { Log.e("CallBackResponse", "onFailure() Request was: " + call.request()); e.printStackTrace(); } @Override public void onResponse(Call call, Response response) throws IOException { Log.i("CallBackResponse ", "onResponse(): " + response.body().string()); } }); } }