De man ssh , que para mim lista essa opção como quinto:
-A Enables forwarding of the authentication agent connection.
This can also be specified on a per-host basis in a configuration file.
Agent forwarding should be enabled with caution. Users with the
ability to bypass file permissions on the remote host
(for the agent's UNIX-domain socket) can access the local agent
through the forwarded connection. An attacker cannot
obtain key material from the agent, however they can perform
operations on the keys that enable them to authenticate
using the identities loaded into the agent.
Veja man ssh_config para os nomes das opções do arquivo de configuração, sem ter Eu acho que você quer ForwardAgent aqui.