Answer: Mutual authentication
Explanation: Also known as two-way authentication, it simply means that both parties identify with each other before any, even this action mentioned in the question. This is the default way to check the data and its authenticity in some protocols, while optional in some other protocols. Basically, mutual authentication is done from machine to machine where mutual users take care of whether or not the remote authentication is successful. Mutual authentication can be with a username and a password, or based on a certificate.