How to change default Laravel Auth login view

In App\Http\Controllers\Auth\LoginController define a fuction named showLoginForm() as:

public function showLoginForm()
{
    return view('custom.login');
}

It overrides the function showLoginForm defined in the trait Illuminate\Foundation\Auth\AuthenticatesUsers.

Note: In Laravel 5.3 the function name is changed from getLogin to showLoginForm.

Since the question was already answered I'll give the same example for the current version of Laravel.

If you're on Laravel 5.6 and up, this functionality should be put in

app/Http/Controllers/Auth/LoginController.php

public function showLoginForm()
{
    return view('custom.login');
}

Also, if you would like to add a parameter to this, you can do so if you specify it in your web route like this:

Route::get('login/{page?}', 'Auth\LoginController@showLoginForm')->name('login');

Then you can do something like this:

public function showLoginForm($page = null)
{
    if(isset($page)){
        // do something
        // example: return view('auth.login', compact('page'));
    }
    return view('auth.login');
}

Tip: if you don't have the LoginController in your project make sure you run

php artisan make:auth