RFC 1416 [14] is an experimental Internet community standard which defines a framework for passing authentication information through the Telnet session. It is intended that the authentication option defined in this RFC is general enough that it can be used to pass information for any authentication system. The description of RFC 1416 given here is quite detailed, as I will extend this standard, and an implementation of it, to support a new authentication type.
Figure 2.7 illustrates the principle of authentication information exchange in the Telnet protocol. First the parties agrees to use the authentication option. Then authentication information is passed in one or both directions. Normally only the client send authentication information.
Figure 2.7: Authentication information exchange