code: @Builder(builderClassName = "ProxiedFileSystemFromKeytab", builderMethodName = "fromKeytab")
    private static FileSystem getProxiedFileSystemUsingKeytab(@NonNull final String userNameToProxyAs,
        final String superUserName, final Path superUserKeytabLocation, final URI fsURI, final Configuration conf,
        FileSystem referenceFS) throws IOException, ExecutionException {
      Preconditions.checkNotNull(userNameToProxyAs, "Must provide a user name to proxy as.");
      Preconditions.checkNotNull(superUserName, "Must provide a super user name.");
      Preconditions.checkNotNull(superUserKeytabLocation, "Must provide a keytab location.");
      URI actualURI = resolveUri(fsURI, conf, referenceFS);
      Configuration actualConfiguration = resolveConfiguration(conf, referenceFS);
  
      return USER_NAME_TO_FILESYSTEM_CACHE.get(getFileSystemKey(actualURI, userNameToProxyAs, referenceFS),
          new CreateProxiedFileSystemFromKeytab(userNameToProxyAs, superUserName, superUserKeytabLocation, actualURI,
              actualConfiguration, referenceFS));
    }
docs: Cached version of {@link ProxiedFileSystemUtils#createProxiedFileSystemUsingKeytab(String, String, Path, URI, Configuration)}.