If I want to use some custom class in Lumen, where should I place them? The Laravel official document does not mention this in any of application structure, service container or package development. Actually I found the document quite confusing to some extents.
For example, I want to set up a service called Invitation, I know I need to register this class in InvitationServiceProvider but where should I place the Invitation.php which the actual class exists in? This package is used for some specific application thus I do not want to put it in composer packagist.
BTW, the version of Lumen Framework is 5.2.
