Flutter Web - Open external url in same tab

I have Flutter Web app and I need to redirect the user out of my app (to a facebook login form) that eventually will redirect the user back to my app. My problem is that I can't open that external url in the same tab with url_launcher (https://pub.dev/packages/url_launcher) because this library launch the url in a new tab and I end up with 2 browser tabs both with my app on it. I tried to use an WebView but the X-Frame options for facebook are set on 'sameorigin' and can't be displayed into an iframe (what the webview does). I need a solution that allows me to redirect the user to Facebook login in the same tab (without using facebook_login_web plugin because I use Spring Social on the server side for this).