code: func (fs *FSLocalKeyStore) GetCertsPEM(proxy string) ([]byte, error) {
  	dir, err := fs.dirFor(proxy, false)
  	if err != nil {
  		return nil, trace.Wrap(err)
  	}
  	return ioutil.ReadFile(filepath.Join(dir, fileNameTLSCerts))
  }
docs: // GetCertsPEM returns trusted TLS certificates of certificate authorities PEM block