Get Sharepoint Permissions\Roles (custom) of a user from AD Group that is part of SP Group via CSOM

SharePoint 2013 + provider-hosted app.

User is part of AD group. AD group is part of Sharepoint group. Sharepoint group has custom security permissions assigned.

How do I check whether user has some custom permission?

The only way I could think of is to get user AD groups and retrieve permissions for these groups from SharePoint.