code: func (fs *FSLocalKeyStore) SaveCerts(proxy string, cas []auth.TrustedCerts) error {
  	dir, err := fs.dirFor(proxy, true)
  	if err != nil {
  		return trace.Wrap(err)
  	}
  	fp, err := os.OpenFile(filepath.Join(dir, fileNameTLSCerts), os.O_CREATE|os.O_RDWR|os.O_TRUNC, 0640)
  	if err != nil {
  		return trace.Wrap(err)
  	}
  	defer fp.Sync()
  	defer fp.Close()
  	for _, ca := range cas {
  		for _, cert := range ca.TLSCertificates {
  			_, err := fp.Write(cert)
  			if err != nil {
  				return trace.ConvertSystemError(err)
  			}
  			_, err = fp.WriteString("\n")
  			if err != nil {
  				return trace.ConvertSystemError(err)
  			}
  		}
  	}
  	return nil
  }
docs: // SaveCerts saves trusted TLS certificates of certificate authorities