Firebase not detecting signed in users - flutter

Question

am trying to create an app whereby at the initial step, users log in and after keying a username and password, the list of users should be reflected in Firebase Authentication screen. I am able to log in with username but the list of users logged in is not reflected...
Please help!
This is my login page code:
import 'package:flutter/material.dart';
import 'package:firebase_auth/firebase_auth.dart';
class Login extends StatefulWidget {
#override
_LoginState createState() => _LoginState();
}
class _LoginState extends State<Login> {
final FirebaseAuth _auth = FirebaseAuth.instance;
final GlobalKey<FormState> _formKey = GlobalKey<FormState>();
String _email, _password;
checkAuthentification() async {
_auth.authStateChanges().listen((user) {
if (user != null) {
print(user);
Navigator.pushReplacementNamed(context, "/");
}
});
}
#override
void initState() {
super.initState();
this.checkAuthentification();
}
login() async {
if (_formKey.currentState.validate()) {
_formKey.currentState.save();
try {
await _auth.signInWithEmailAndPassword(
email: _email, password: _password);
} catch (e) {
showError(e.message);
print(e);
}
}
}
showError(String errormessage) {
showDialog(
context: context,
builder: (BuildContext context) {
return AlertDialog(
title: Text('ERROR'),
content: Text(errormessage),
actions: <Widget>[
FlatButton(
onPressed: () {
Navigator.of(context).pop();
},
child: Text('OK'))
],
);
});
}
#override
Widget build(BuildContext context) {
return Scaffold(
body: SingleChildScrollView(
child: Container(
child: Column(
children: <Widget>[
Container(
child: Form(
key: _formKey,
child: Column(
children: <Widget>[
SizedBox(height: 300),
Container(
child: TextFormField(
validator: (input) {
if (input.isEmpty) return 'Enter Email';
},
decoration: InputDecoration(
labelText: 'Email',
prefixIcon: Icon(Icons.email)),
onSaved: (input) => _email = input),
),
Container(
child: TextFormField(
validator: (input) {
if (input.length < 6)
return 'Provide Minimum 6 Characters';
},
decoration: InputDecoration(
labelText: 'Password',
prefixIcon: Icon(Icons.lock),
),
obscureText: true,
onSaved: (input) => _password = input),
),
SizedBox(height: 20),
RaisedButton(
padding: EdgeInsets.fromLTRB(70, 10, 70, 10),
onPressed: login,
child: Text('LOGIN',
style: TextStyle(
color: Colors.white,
fontSize: 20.0,
fontWeight: FontWeight.bold)),
color: Colors.orange,
shape: RoundedRectangleBorder(
borderRadius: BorderRadius.circular(20.0),
),
)
],
),
),
),
],
),
),
));
}
}