public function validateCredentials(UserContract $user, array $credentials)
    {
        $plain = $credentials[\'password\'];
        return $this->hasher->c         
        You can create your own UserProvider and then you can override the functions from the original UserProvider.
First you create the CustomUserProvider:
use Illuminate\Contracts\Auth\UserProvider;
use Illuminate\Contracts\Auth\Authenticatable as UserContract;
class CustomUserProvider extends UserProvider {
  public function validateCredentials(UserContract $user, array $credentials)
  {
    $plain = $credentials['password'];
    return $this->hasher->check($plain, $user->getAuthPassword());
  }
}
Then you register your new CustomUserProvider in config/app.php
'providers' => array(
   ... On the bottom, must be down to override the default UserProvider
   'Your\Namespace\CustomUserProvider'
),
                                                                        In Laravel 5.4 you don't need to register your CustomUserProvider in config/app.php.
See this blog article for detailed instructions.
The short form:
First, create a CustomUserProvider.php file in your Providers directory:
<?php
namespace App\Providers;
use Illuminate\Auth\EloquentUserProvider as UserProvider;
use Illuminate\Contracts\Auth\Authenticatable as UserContract;
class CustomUserProvider extends UserProvider {
    public function validateCredentials(UserContract $user, array $credentials)
    {
        $plain = $credentials['password'];
        return $this->hasher->check($plain, $user->getAuthPassword());
    }
}
After this, change the boot() Method in your AuthServiceProvider.php file:
public function boot()
{
    $this->registerPolicies();
    \Illuminate\Support\Facades\Auth::provider('customuserprovider', function($app, array $config) {
        return new CustomUserProvider($app['hash'], $config['model']);
    });
}
Now, you can use the provider by adding the driver name to your config/auth.php file:
'providers' => [
    'users' => [
        'driver' => 'customuserprovider',
        'model' => App\User::class,
        'table' => 'users',
    ],
],