code: @Builder(builderClassName = "ProxiedFileSystemFromToken", builderMethodName = "fromToken")
    private static FileSystem getProxiedFileSystemUsingToken(@NonNull String userNameToProxyAs, Token<?> userNameToken,
        URI fsURI, Configuration conf, FileSystem referenceFS) throws IOException, ExecutionException {
      Preconditions.checkNotNull(userNameToProxyAs, "Must provide a user name to proxy as.");
      Preconditions.checkNotNull(userNameToken, "Must provide token for user to proxy.");
      URI actualURI = resolveUri(fsURI, conf, referenceFS);
      Configuration actualConfiguration = resolveConfiguration(conf, referenceFS);
  
      return USER_NAME_TO_FILESYSTEM_CACHE.get(getFileSystemKey(actualURI, userNameToProxyAs, referenceFS),
          new CreateProxiedFileSystemFromToken(userNameToProxyAs, userNameToken, actualURI, actualConfiguration,
              referenceFS));
    }
docs: Cached version of {@link ProxiedFileSystemUtils#createProxiedFileSystemUsingToken(String, Token, URI, Configuration)}.