默認是使用eloquent作為認證驅動器，所以看看Illuminate\Auth\EloquentUserProvider里面的實現
public function validateCredentials(UserContract $user, array $credentials)
{
$plain = $credentials['password'];

return $this->hasher->check($plain, $user->getAuthPassword());
}

所以如果要改驗證的邏輯，可以繼承原有的驅動器，然后重寫validateCredentials里面的邏輯
class TestUserProvider extend EloquentUserProvider
{
public function validateCredentials(UserContract $user, array $credentials)
{
$plain = $credentials['password'];

return md5($plain) == $user->getAuthPassword();
}
}

最后設置驅動器，建議加載AppServiceProvider的boot()里面
Auth::setProvider(new TestUserProvider());