How to auto login users after first login in a simple Webview app android

Question

At first I wanna say thanks for your attention.

I have a simple web view (client) app and I want to set an option that can auto login user after the first time that user logged in...
It means when user closed the app and reopen that it have been stay logged in
I have checked many topics in stack and ... but I just understand to use cookies but don't know how to use...

public class MainActivity extends AppCompatActivity {

    private WebView webView;
    FloatingActionButton fab;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        check();
        webclient();
        navcolor();
        onesignal();



        fab = findViewById(R.id.fab);
        fab.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                webView.loadUrl("http://www.datalifeengine.ir/");
                Toast.makeText(MainActivity.this, "homepage...", Toast.LENGTH_SHORT).show();
            }
        });


        String url;
        Intent intent = getIntent();
        String action = intent.getAction();
        Uri data = intent.getData();


        if (data != null) {
            webView.loadUrl(data.getScheme() + "://" + data.getHost() + data.getPath());
        } else {
            webView.loadUrl("http://www.datalifeengine.ir/");
        }

    }


    @Override
    public void onBackPressed() {

        if (webView.canGoBack()) {
            webView.goBack();
        } else {
            super.onBackPressed();
        }
    }

    public void navcolor() {
        if (android.os.Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
            getWindow().setNavigationBarColor(ContextCompat.getColor(this, R.color.colorPrimaryDark));
        }
    }

    public void webclient() {
        webView = (WebView) findViewById(R.id.webview);
        webView.setWebViewClient(new WebViewClient());
        webView.getSettings().setJavaScriptEnabled(true);
        webView.getSettings().setLoadWithOverviewMode(true);
        webView.getSettings().setUseWideViewPort(true);
        webView.getSettings().setBuiltInZoomControls(true);

    }

    void check() {
        ConnectivityManager conMgr = (ConnectivityManager) getSystemService(Context.CONNECTIVITY_SERVICE);

        if (conMgr.getNetworkInfo(ConnectivityManager.TYPE_MOBILE).getState() == NetworkInfo.State.CONNECTED
                || conMgr.getNetworkInfo(ConnectivityManager.TYPE_WIFI).getState() == NetworkInfo.State.CONNECTED) {

            Toast.makeText(this, "online", Toast.LENGTH_SHORT).show();
        } else if (conMgr.getNetworkInfo(ConnectivityManager.TYPE_MOBILE).getState() == NetworkInfo.State.DISCONNECTED
                || conMgr.getNetworkInfo(ConnectivityManager.TYPE_WIFI).getState() == NetworkInfo.State.DISCONNECTED) {

            Toast.makeText(this, "offline", Toast.LENGTH_SHORT).show();
        }
    }

    public void onesignal(){
        OneSignal.startInit(this)
                .inFocusDisplaying(OneSignal.OSInFocusDisplayOption.Notification)
                .unsubscribeWhenNotificationsAreDisabled(true)
                .init();

    }


}