We have devices that can generate tokens. So we can use tokens with passwords to perform two factor authentication. There are many ways to implement such systems to enhance security. One of two I know, is to modify open-ssh client, and, another is to develop a PAM(Pluggable authentication module) module.
Are there other ways? Which is the best method considering easy deployment (note: complexity of development is not concern)? The authentication will be used mainly by server's ssh daemon to authenticate users for log in.