code: func (c *Config) CheckACL() error {
  	switch c.ACLDefaultPolicy {
  	case "allow":
  	case "deny":
  	default:
  		return fmt.Errorf("Unsupported default ACL policy: %s", c.ACLDefaultPolicy)
  	}
  	switch c.ACLDownPolicy {
  	case "allow":
  	case "deny":
  	case "async-cache", "extend-cache":
  	default:
  		return fmt.Errorf("Unsupported down ACL policy: %s", c.ACLDownPolicy)
  	}
  	return nil
  }
docs: // CheckACL validates the ACL configuration.