cli/cli/documentation/en_US/aaa/aaa-authentication-example

aaa authentication login default group tacacs+
  Use TACACS+ for authenticating SSH CLI logins

aaa authentication login default local
  Use local UNIX /etc/passwd for authenticating SSH CLI logins.

aaa authentication login default group tacacs+ local
  Use both TACACS+ and /etc/passwd for login.

no aaa authentication login default
  Reset authentication sources for SSH CLI login.