I've started to use Drupal 8 and some modules requires some libraries.
For example search api solr. When I'm installing these libraries via composer it downloads the libraries into directory of the module.
For example modules/contrib/search\_api\_solr/vendor.
I don't think that it's correct because contrib modules should be stored in clean state.

What the right way to install libraries for modules via composer?
Where should I store them?