How to Login Registered Users to a Backendless App Using the User Login API

package samples.mbaas.com.cookbook;
import com.backendless.Backendless;
import com.backendless.BackendlessUser;
import com.backendless.async.callback.AsyncCallback;
import com.backendless.exceptions.BackendlessFault;
public class MainActivity extends AppCompatActivity {
    private static String APPID = "YOUR-APP-ID";
    private static String APIKEY = "YOUR-ANDROID-API-KEY";
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Backendless.initApp(this, APPID, APIKEY);
        Backendless.UserService.login(
                "green.goblin@backendless.com",
                "sp1dey",
                new AsyncCallback<BackendlessUser>() {
                    @Override
                    public void handleResponse(BackendlessUser response) {
                        Toast.makeText(getContext(), "User has been logged in", Toast.LENGTH_LONG).show();
                    }
                    @Override
                    public void handleFault(BackendlessFault fault) {
                        Toast.makeText(getContext(), fault.getMessage(), Toast.LENGTH_LONG).show();
                    }
                });
    }
    public Context getContext() {
        return this;
    }
}

Backendless.UserService.login("green.goblin@backendless.com", "sp1dey",
   object : AsyncCallback<BackendlessUser> {
       override fun handleResponse(user: BackendlessUser?) {
           Log.i(TAG, "User has been logged in")
       }

       override fun handleFault(fault: BackendlessFault?) {
           Log.e(TAG, fault?.message)
       }
   })

[Backendless.shared.userService loginWithIdentity:@"spidey@backendless.com" password:@"greeng0blin" responseHandler:^(BackendlessUser *loggedInUser) {
    NSLog(@"User has been logged in: %@", loggedInUser);
} errorHandler:^(Fault *fault) {
    NSLog(@"Error: %@", fault.message);
}];

Backendless.shared.userService.login(identity: "spidey@backendless.com", password: "greeng0blin", responseHandler: { loggedInUser in
    print("User has been logged in: \(loggedInUser)")
}, errorHandler: { fault in
    print("Error: \(fault.message ?? "")")
})

const Backendless = require('backendless')
/*
 Or use `import Backendless from 'backendless'` for client side.
 If you don't use npm or yarn to install modules, you can add the following line
 <script src="//api.backendless.com/sdk/js/latest/backendless.min.js"></script>
 to your index.html file and use the global Backendless variable.
*/

Backendless.initApp('YOUR_APP_ID', 'YOUR_JS_API_KEY')

const onSuccess = user => {
  console.log('User has been logged in:\n', user)
}

const onError = error => {
  console.error('Server reported an error: ', error.message)
  console.error('error code: ', error.code)
  console.error('http status: ', error.status)
}

Backendless.UserService.login('spidey@backendless.com', 'greeng0blin')
  .then(onSuccess)
  .catch(onError)

Backendless.UserService.login("green.goblin@backendless.com", "sp1dey").then(
   (user) => print("User has been logged in"));