How about the owncloud module for managing cloud space
Exists via third party module: https://marketplace.blesta.com/#/extensions/133-Nextcloud%20Module
is that the same as OwnCloud?
Given that nextcloud is an owncloud fork, means the api (at least for provisioning purposes) is the same.
https://docs.nextcloud.com/server/latest/admin_manual/configuration_user/instruction_set_for_users.html
https://doc.owncloud.com/server/next/developer_manual/core/apis/provisioning-api.html#add-user
So the module linked can provision accounts both on own as well as nextcloud.
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I like this idea 
Exists via third party module: https://marketplace.blesta.com/#/extensions/133-Nextcloud%20Module
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