SID mapping

As mentioned in the Intro to Cygwin page, Cygwin is able to give POSIX binaries the ability to authenticate to the Windows SID subsystem.

To take advantage of this feature for:

SSH authentication
Install the OpenSSH daemon according to SSHD

Be sure to set the CYGWIN variable for the daemon to 'ntsec'

Windows usernames with spaces
According to the Cygwin FAQ, these usernames will cause problems for Cygwin. Avoid using them.

From the official Cygwin documentation
Using Windows security in Cygwin