无法在laravel中实现authenticate方法

I am not able to make a user login in Laravel. I am using username instead of email.

Below is my Routes

use App\Message;

Route::get('/', function () {
    return view('welcome');
});
//


Route::post('/contact','MessageController@store');

Route::get('/admin9419/dashboard','AdminDashboardController@index')->name('dash');
Route::get('/admin9419/login','SessionsController@create')->name('home');
Route::post('/admin9419/login','SessionsController@store');
Route::post('/admin9419/logout','SessionsController@destroy');

This is my SessionController File

<?php

namespace App\Http\Controllers;

use Illuminate\Http\Request;
use Illuminate\Foundation\Auth\AuthenticatesUsers;

class SessionsController extends Controller
{



    public function __construct()
    {

        $this->middleware('guest');

    }


    public function create(){


        return view('sessions.create');


    }


    public function destroy(){

        auth()->logout();

        return redirect()->home();

    }

    public function store(){



       if(!auth()->attempt(['username'=>request('username'),'password'=>request('password')])){

           return back();

       }

       return redirect('/admin9419/dashboard');


    }

}

Error:

Type error: Argument 1 passed to Illuminate\Auth\EloquentUserProvider::validateCredentials() must be an instance of Illuminate\Contracts\Auth\Authenticatable

User class:

<?php

namespace App;

use Illuminate\Database\Eloquent\Model;

class User extends Model
{
    //
}

Can anyone help what i missed?

The code seems correct.

See the Class User that it should be something like:

 use App\Notifications\MailResetPasswordToken;
use Illuminate\Notifications\Notifiable;
use Illuminate\Foundation\Auth\User as Authenticatable;

class User extends Authenticatable
{
    use Notifiable;
    ....
}

So can you paste the User class?

By default, Laravel uses the email field for authentication. If you would like to customize this, you may define a username method on your LoginController:

public function username()
{
    return 'username';
}

From : https://laravel.com/docs/5.5/authentication

public function store(Request $request){

  $username= $request->input('username');
  $password= $request->input('password');

  if (Auth::guard('web')->attempt(['username' => $username , 'password'=> $password ])) {
         return redirect()->intended('/admin9419/dashboard');
  }
  else{
   return redirect('/login');
  }
}