Multi-tenant / Multi-instance federated custom user groups

[github-canni]

While owncloud file/folder-sharing supports multi-tenant/multiple instances (Federated Cloud Sharing) to find registered users on multiple servers and share with them, the custom groups feature does not.

Users are only able to create custom groups with users on their own instance and not foreign federated instances.

Feature Request:

• Add autocomplete/search for federated users to "Add user to this group"- field in custom groups section

• Allow federated users to be added to custom group / assigned a role in that group