Oracle Solaris 10 has been an amazing OS update, including ground breaking features like Zones (Solaris Containers), ZFS, Services, Dynamic Tracing (against live production operating systems without impact), and Logical Domains. These features have been emulated by the market (imitation is the finest form of flattery!)
Solaris 10: End of Life
As with all good things, they must come to an end. Sun Microsystems was purchased by Oracle and eventually, the greatest OS known to the industry needed to be updated. Oracle set a retirement date of January 2021. Oracle had indicated an uplift in support costs would be needed, for Solaris 10 systems.
Solaris 10: Extended Support to 2024
No migration tools were ever provided by Oracle to facilitate migration
from Solaris 10 to Solaris 11, so migration to Solaris has been slow. Oracle had decided in September 2019 that Extended Support for Solaris 10, without additional financial penalty, would be delayed to 2024!
In the early days of the internet, the file transfer mode of choice was FTP. This had remained the internet standard for many years, until the need for encryption had become so prevalent. SFTP happens to be one option for delivering files.
A good reference on creating an SFTP server can be see on this web site. This is not isolated to Linux, but can be used under SVR4 & POSIX systems like Solaris, or other Open Sourced based operating systems based upon OpenSolaris or Illumos.
Usually if SFTP is all that is desired to be granted, one should not allow standard TTY based logins. One option is to set up a shell using the "nologin" binary. A quick reference on using "nologin" vs other binaries like "false". In early UNIX days, "sync" was sometimes used!