pixelfed/app/Http/Controllers/Auth/LoginController.php

<?php

namespace App\Http\Controllers\Auth;

use App\Http\Controllers\Controller;
use Illuminate\Foundation\Auth\AuthenticatesUsers;

class LoginController extends Controller
{
    /*
    |--------------------------------------------------------------------------
    | Login Controller
    |--------------------------------------------------------------------------
    |
    | This controller handles authenticating users for the application and
    | redirecting them to your home screen. The controller uses a trait
    | to conveniently provide its functionality to your applications.
    |
    */

    use AuthenticatesUsers;

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

    /**
     * Create a new controller instance.
     *
     * @return void
     */
    public function __construct()
    {
        $this->middleware('guest')->except('logout');
    }

    /**
     * Validate the user login request.
     *
     * @param  \Illuminate\Http\Request  $request
     * @return void
     */
    public function validateLogin($request)
    {
        $rules = [
            $this->username() => 'required|string',
            'password' => 'required|string',
        ];

        if(config('pixelfed.recaptcha')) {
            $rules['g-recaptcha-response'] = 'required|recaptcha';
        }

        $this->validate($request, $rules);
    }
}