No, it's not possible.
Cygwin mimics Unix and provides
/etc/group, but make no mistake, Cygwin needs and uses standard Windows user accounts.
/etc/group are populated to reflect this.
useradd in Cygwin.
Cygwin does a great job as a Linux-like environment, but it's not an operating system. It uses Windows users/groups and the standard Windows security model (see http://cygwin.com/cygwin-ug-net/ntsec.html):
(...) the Windows security model is utilized in
Cygwin to implement POSIX-like permissions (...) The Windows
authentication model is used to allow cygwin applications to switch
users in a POSIX-like fashion.
For example, in Configuring Cygwin on a Windows server we can read:
Create the accounts that will be able to log in [using CYGWIN sshd] to the computer:
- Create the Windows accounts first. Click Start > Settings > Control Panel > User Accounts. Make each user a member of the
Administrators group. (...)
That all means that you're stuck with using Windows accounts for authentication, also for