SSHD and PAM

[Sudarshan Soma]

Hi I am trying to write pam_radius module which talks to RADIUS server for
aaa.

I see sshd checks /etc/passwd for user list. Since RADIUS server has user
list, can sshd ignore this check for RADIUS/TACACS+ authentication, Please
suggest if there are any flags to control it.

I am using the following versions.
OpenSSH_6.6p1, OpenSSL 1.0.2n  7 Dec 2017

I see sssd (NAS) being used for such use cases, how does sshd ignore
/etc/passwd in those cases.
Please suggest

Regards,
Ivan.