code: func SSHAgentClient() (gosshagent.Agent, error) {
  	sock := os.Getenv("SSH_AUTH_SOCK")
  	if sock == "" {
  		return nil, errors.New("SSH_AUTH_SOCK environment variable is not set. Verify ssh-agent is running. See https://github.com/coreos/fleet/blob/master/Documentation/using-the-client.md for help.")
  	}
  
  	agent, err := net.Dial("unix", sock)
  	if err != nil {
  		return nil, err
  	}
  
  	return gosshagent.NewClient(agent), nil
  }
docs: // SSHAgentClient returns an Agent that talks to the local ssh-agent