[Samba] Need workaround or replacement of "security = server" in SAMBA 4

[Goetz, Roland]

Hello SAMBA developers,

In our R&D environment we are using 500+ workstations and 30+ servers running RedHat Linux.
We are using RHEL 3,4,5  with SAMBA 3.0.x , RHEL 6 with SAMBA 3.6.9 and now we are testing migration to RHEL7.
On each of the 500+ workstations and 10+ servers we have SAMBA server running with "security = server", "password server = <Name or IP of DomainController> ", "encrypt passwords = Yes" and "username map = /etc/samba/smbusers".  This worked perfectly on all of our workstations and servers from RHEL3 through RHEL6 !!
But now with RHEL7 only SAMBA 4 is available and "security = server" is no longer there.
Our Windows environment is completely managed by our IT and we are not able or allowed to add domain members and we often need to re-install our workstations so we cannot add the workstation to the domain.
Is there any possibility to allow our Linux users to access SAMBA shares (inclusive [homes]) on each workstation and server from their Windows PCs (Win 7 mainly) with getting authenticated automatically by the existing Windows DC or LDAP?

Thanks and kind regards
Roland Goetz