Is there a solution for secure teamwork in GoogleDocs or Office365 or something like that?

Question

SharePoint

There is a need to store in the cloud and it is desirable to edit business-critical documents.
Access to these documents is provided to several persons.
Basic requirements:
1) not stored locally in the browser cache
2) the ability to edit in the browser
3) access by some kind of iron etoken
4) must work on MAC and Windows
It is possible to put your own server for this, Windows / Linux does not matter.
The current implementation of this task as a few shared documents in GoogleDocs suits everyone except the level of protection.

Answer 1

Found by the way probably a good solution.
etoken PRO for IIS 7.0 + SSL from its own PKI in AD
and on IIS will deploy the package www.onlyoffice.com/ru/server.aspx
Cloud file storage and editors, etc.
Everything under the GPL.

Answer 2

There are no such solutions in the context of msoffis support, or some partial custom solutions for the client, well, the price of such solutions is enterprise and the amount with many zeros in bucks.