laravel 5 authentication errors

So i have some problem with laravel 5 login authentication.I'm have try everyway but the only result i get it's false when the code run to if($this-> auth -> attempt($auth)) statement .So what i have been missing.Here it's the code

UserController.php

<?php namespace App\Http\Controllers;

use App\Users;
use App\Http\Controllers\Controller;
use App\Http\Requests\FormValRequest;
use App\Http\Requests\Request;
use Illuminate\Contracts\Auth\Guard;
use Illuminate\Contracts\Auth\Registrar;
use Illuminate\Foundation\Auth\AuthenticatesAndRegistersUsers;
use Auth;
use Hash;

class UsersController extends Controller {

    public function __construct(Guard $auth, Registrar $registrar)
    {
        $this->auth = $auth;
        $this->registrar = $registrar;
        $this->middleware('guest', ['except' => 'getLogout']);
    }

    /**
     * Sign in function to validate input
     *
     * @return if success return to index page 
     * else return error message
    */
    use AuthenticatesAndRegistersUsers;

    public function login(FormValRequest $request)
    {
        $auth = array(
            'username' => $request -> txtUsernameLogin,
            'password' => $request -> txtPasswordLogin
        );
        if($this-> auth -> attempt($auth))
        {
            echo "success";
        }
        else
        {
            echo "fail";

        }

    }
}

Routes.php

Route::post('authen/login',['as' => 'login','uses'=>'UsersController@login']);

FormValRequest.php

<?php namespace App\Http\Requests;

use App\Http\Requests\Request;

class FormValRequest extends Request {

    /**
     * Determine if the user is authorized to make this request.
     *
     * @return bool
     */
    public function authorize()
    {
        return true;
    }

    /**
     * Get the validation rules that apply to the request.
     *
     * @return array
     */
    public function rules()
    {
        return [
            'txtUsernameLogin' => 'required',
            'txtPasswordLogin' => 'required',
        ];
    }

    public function messages()
    {
        return [
            'txtUsernameLogin.required' => 'Please input your username',
            'txtPasswordLogin.required' => 'Please input your password',
        ];
    }

}

And the view footer.blade.php(i'm using bootstrap popup modal )

        <form  action="{{ url('/authen/login') }}" method="POST" name="SignInForm">
        <input type="hidden" name="_token" value="{!! csrf_token() !!}">
            <ul class="social-login">
                <li><a class="btn btn-facebook"><i class="fa fa-facebook"></i>Sign In with Facebook</a></li>
                <li><a class="btn btn-google"><i class="fa fa-google-plus"></i>Sign In with Google</a></li>
                <li><a class="btn btn-linkedin"><i class="fa fa-linkedin"></i>Sign In with LinkedIn</a></li>
            </ul>
            <hr>
            <div class="form-group">
                <label for="login-username">Username</label>
                <input type="text" class="form-control" id="txtUsernameLogin" name="txtUsernameLogin">
                {!! $errors -> first('txtUsernameLogin') !!}
            </div>
            <div class="form-group">
                <label for="login-password">Password</label>
                <input type="password" class="form-control" id="txtPasswordLogin" name="txtPasswordLogin">
                {!! $errors -> first('txtPasswordLogin') !!}
            </div>
            <button type="submit" class="btn btn-primary">Sign In</button>
        </form>

via Chebli Mohamed