Laravel : Login not working after defined custom routes for admin in routes/admin.php

Im using laravel 5.7 , I want to separate route for user and admin , so i have created file routes/admin.php

Route::group(['namespace' => 'Admin\Dashboard'],function () {
    Route::get('/','DashboardController@index')->name('admin.dashboard');
    Route::post('/top_categories','DashboardController@topCategories')->name('admin.top_categories');
});


Route::group(['namespace' => 'Admin\Auth'],function () {
    Route::get('/login','LoginController@showAdminLoginForm')->name('admin.login');
    Route::post('/login','LoginController@adminLogin');
    Route::post('/logout', 'LoginController@logout')->name('admin.logout');
    Route::get('/register','RegisterController@showAdminRegisterForm')->name('admin.register');
    Route::post('/register', 'RegisterController@createAdmin');
    Route::get('/forgot-password','ForgotPasswordController@showForgotPassword')->name('admin.forgot-password');
    Route::post('/forgot-password', 'ForgotPasswordController@sendResetLinkEmail')->name('admin.send-reset-email');
});

and in RouteServiceProvider.php

public function map()
{
    $this->mapApiRoutes();
    $this->mapWebRoutes();
    $this->mapAdminRoutes();
}

protected function mapAdminRoutes(){
    Route::middleware('web')
    ->namespace($this->namespace)
    ->prefix('admin')
    ->group(base_path('routes/admin.php'));
}

But After this , I am unable to login for Both user and admin , the page redirect back to login page even if i enter correct credentials , previously it is working correct when i haven't created separated file for admin

Here is code for AdminLoginController :

<?php

namespace App\Http\Controllers\Admin\Auth;

use Illuminate\Http\Request;
use App\Http\Controllers\Controller;
use Illuminate\Foundation\Auth\AuthenticatesUsers;
use Illuminate\Support\Facades\Auth;

class LoginController extends Controller
{


    use AuthenticatesUsers;

    /**
     * Where to redirect users after login.
     *
     * @var string
     */
    protected $redirectTo = '/admin';


    public function __construct()
    {
        $this->middleware('guest:admin')->except('logout');
    }

    public function showAdminLoginForm()
    {
        return view('admin.auth.login');
    }

    public function adminLogin(Request $request)
    {
        $this->validate($request, [
            'email'   => 'required|email',
            'password' => 'required|min:6'
        ]);
        if (Auth::guard('admin')->attempt(['email' => $request->email, 'password' => $request->password], $request->get('remember'))) {
            return redirect()->intended(route('admin.dashboard'));
        }
        return back()->withInput($request->only('email', 'remember'));
    }


    public function logout(Request $request)
    {
        $this->guard()->logout();
        $request->session()->flush();
        $request->session()->regenerate();
        return redirect()->route('admin.login');
    }
}

I Have also tried to clear route cache : php artisan route:clear but no luck :(

anyone please help me to solve this issue .

via Chebli Mohamed