code: def check_and_load_ssh_auth():
      
  
      mac_username = get_config_value(constants.CONFIG_MAC_USERNAME_KEY)
      if not mac_username:
          logging.info("Can't setup ssh authorization; no mac_username specified")
          return
      if not _running_on_mac(): # give our Linux unit tests a way to not freak out
          logging.info("Skipping SSH load, we are not running on Mac")
          return
  
      if _mac_version_is_post_yosemite():
          _load_ssh_auth_post_yosemite(mac_username)
      else:
          _load_ssh_auth_pre_yosemite()
docs: Will check the mac_username config value; if it is present, will load that user's
      SSH_AUTH_SOCK environment variable to the current environment.  This allows git clones
      to behave the same for the daemon as they do for the user