For a long time now, Meshcentral.com has been able to handle having a mesh of computers shared between many web accounts. Sadly, there was no good way to add and remove user access to a mesh. You had to use the MeshConnector tool which was Windows only, etc. Well things just god a lot better! I added the new account add/remove feature so you can now create a mesh and control which user get access to it. You can also set the user privilages: "administrator" and "viewer".
To add user access, go to the account tab, click on a mesh. At the bottom of the page you see the list of users that can view or access computers on this mesh. Click the add link to add new users or the trash icon to remove them.
Just make sure to grant access to the correct user. Also, I don't have more granular access control, so you can't grant access to only one computer, just the entire mesh. But hopefully, I will be working on that in the future.