UserRefreshExample.java

final String clientId = "***", clientSecret = "***", redirectUrl = null;
final TwitchIdentityProvider tip = new TwitchIdentityProvider(clientId, clientSecret, redirectUrl);

Supplier<OAuth2Credential> readCredentialFromFile = () -> {
    final String initialAccessToken = "***", initialRefreshToken = "***"; // TODO: must be read from file
    final OAuth2Credential cred = new OAuth2Credential("twitch", initialAccessToken);
    cred.setRefreshToken(initialRefreshToken);
    return cred;
};

Consumer<OAuth2Credential> saveCredentialToFile = token -> {
    // TODO: save to the same file
};

final OAuth2Credential initialToken = readCredentialFromFile.get();
OAuth2Credential credential = tip.getAdditionalCredentialInformation(initialToken)
    .orElseGet(() -> tip.refreshCredential(initialToken).flatMap(tip::getAdditionalCredentialInformation).orElse(null));
if (credential == null) {
    throw new RuntimeException("Invalid token!");
} else if (credential != initialToken) {
    saveCredentialToFile.accept(credential);
}

ScheduledThreadPoolExecutor exec = ThreadUtils.getDefaultScheduledThreadPoolExecutor("twitch4j", Runtime.getRuntime().availableProcessors());

if (credential.getExpiresIn() > 0) {
    exec.scheduleAtFixedRate(() -> tip.refreshCredential(credential).ifPresent(cred -> {
        credential.updateCredential(cred);
        saveCredentialToFile.accept(credential);
    }), credential.getExpiresIn() / 2, Duration.ofHours(1L).getSeconds(), TimeUnit.SECONDS);
}

CredentialManager credentialManager = CredentialManagerBuilder.builder().build();
credentialManager.registerIdentityProvider(tip);

ITwitchClient twitchClient = TwitchClientPoolBuilder.builder()
    .withClientId(clientId)
    .withClientSecret(clientSecret)
    .withRedirectUrl(redirectUrl)
    .withCredentialManager(credentialManager)
    .withChatAccount(credential)
    .withDefaultAuthToken(credential)
    .withEnableChat(true)
    .withEnableHelix(true)
    .withEnableChatPool(true)
    .withScheduledThreadPoolExecutor(exec)
    .build();