/**
 * Verifies the user's credentials and performs U2F authentication.
 */
public class SignInActivity
        extends Activity
        implements SurePassIdU2fSign.Listener {
    public static final String U2F_SERVER_URL = "https://fidocert.surepassid.com/server.aspx";

    ///////////////////////
 // working variables //
 ///////////////////////
  private SurePassIdU2fSign mU2fSign;

    private VerifyUsernamePasswordTask mVerifyUsernamePasswordTask = null;

    ///////////////////
 // UI references //
 ///////////////////
  private EditText mUsernameView;
    private EditText mPasswordView;
    private TextView mStatusMessageView;
    private Button mSignInButton;

    /**
 * Initiate U2F Sign.
 */
  private void doU2f() {
        mU2fSign.u2fSign(U2F_SERVER_URL, mUsernameView.getText().toString());
    }

    /**
 * The U2F Sign was successful. Now go to the desired activity.
 */
  @Override
  public void gotoTargetActivity() {
        Intent intent = new Intent(this, TargetAppActivity.class);
        startActivity(intent);
    }

    /**
 * The user is requesting to use an alternate method for second factor authentication.
 * This alternate method is up to the relying party app.
 */
  @Override
  public void gotoAlternateVerificationActivity() {
        Intent intent = new Intent(this, VerificationActivity.class);
        startActivity(intent);
    }

    /**
 * The user aborted the sign in.
 */
  @Override
  public void u2fSignCanceled() {
        displayMessage("Sign In canceled.");
    }

    /**
 * An error occurred during processing.
 * 
 * @param errorMessage The error that occurred.
 */
  @Override
  public void u2fSignError(CharSequence errorMessage) {
        displayMessage(errorMessage);
    }

    @Override
  protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        initUi();

        // Create the U2F Sign object to be used.
  mU2fSign = new SurePassIdU2fSign(this, this);
    }

    /**
 * Call the U2F Sign's onActivityResult method.
 * @param requestCode
  * @param resultCode
  * @param intent
  */
  @Override
  public void onActivityResult(int requestCode, int resultCode, Intent intent) {
        mU2fSign.onActivityResult(requestCode, resultCode, intent);
    }

    /**
 * Initialize the user interface.
 */
  private void initUi() {
        mStatusMessageView = (TextView) findViewById(R.id.status_message);
        mUsernameView = (EditText) findViewById(R.id.username);
        mPasswordView = (EditText) findViewById(R.id.password);

        mSignInButton = (Button) findViewById(R.id.button_sign_in);
        mSignInButton.setOnClickListener(new View.OnClickListener() {
            @Override
  public void onClick(View view) {
                doSignIn();
            }
        });
    }

    /**
 * Called when the Sign In button is pressed.
 */
  private void doSignIn() {
        disableForm();

        String username = mUsernameView.getText().toString();
        String password = mPasswordView.getText().toString();

        // Verify username an password on server.
        mVerifyUsernamePasswordTask = new VerifyUsernamePasswordTask(new AsyncTaskListener() {
            @Override
  public void onAsyncTaskFail(String errorMessage) {
                mPasswordView.requestFocus();
                mPasswordView.selectAll();
                displayMessage(errorMessage);
            }

            /**
 * Called when the username and password have successfully validated.
 * It then calls U2F Sign.
 */
  @Override
  public void onAsyncTaskSuccess() {
                Log.v(TAG, "onAsyncTaskSuccess([]): START");
                doU2f();
            }
        });
        mVerifyUsernamePasswordTask.execute(username, password);
    }

    protected void displayMessage(CharSequence message) {
        mStatusMessageView.setText(message);
    }
}