README

Kilden PHP SDK

Server-side PHP SDK for Kilden, the open customer data platform: events, identity verification and feature flags from your backend. PHP 7.4+, zero dependencies — it runs on the shared hosting your WordPress client lives on and on your Laravel 13 app alike.

composer require kilden/kilden-php:@alpha
# (the @alpha flag goes away at 0.1.0)

$kilden = new Kilden\Client('sk_your_secret_key');

$kilden->track('user_42', 'order_completed', [
    'revenue' => 99.9,
    'currency' => 'CLP',
]);

That is a complete, working integration: events queue in memory and flush in batches (20 events or 10 seconds, whichever comes first), with gzip, retries with backoff, and a shutdown hook that delivers whatever is left after your response is sent — under FPM it runs after fastcgi_finish_request(), so telemetry never adds latency your user can feel.

Use the secret key (sk_), never the public one. Events sent with the secret key are source=server, verified=true — facts your campaigns and revenue reports can trust. The constructor rejects public (wk_) keys outright. Keep the secret key out of browsers, mobile apps, and frontend bundles of any kind.

Identity verification

Anyone can open a browser console and send events as user_id=ceo@corp — unless you turn on identity verification. Your backend signs a short-lived token vouching for the logged-in user; Kilden's web SDK attaches it, and the platform marks those events verified. Signing is the part only your backend can do, and it is three lines:

$signer = new Kilden\IdentitySigner($_ENV['KILDEN_IDENTITY_SECRET'], ['kid' => 'k1']);

$token = $signer->sign($user->id, [
    'ttl'    => 3600,
    'traits' => ['plan' => $user->plan],   // signed traits override unsigned ones
]);

Only sign a sub your backend authenticated. Signing request input — $signer->sign($_POST['user_id']) — lets anyone impersonate anyone, with a "verified" stamp on top. Sign $user->id after your auth layer resolved it, never before.

Traits passed to sign() become signed traits: during enrichment they win over any unsigned traits the browser claims for the same event.

Feature flags

if ($kilden->isEnabled('new_checkout', 'user_42')) {
    // ...
}

$variant = $kilden->getFeatureFlag('pricing_test', 'user_42', [
    'person_properties' => ['plan' => 'pro'],  // evaluated server-side, this call only
    'default'           => false,              // returned if Kilden is unreachable
]);

getFeatureFlag returns false, true, or the variant key as a string. Evaluation is remote against /decide with a 30-second in-memory cache per distinct_id; calls with person_properties bypass the cache. When Kilden cannot answer within timeout (default 3s), you get your default back — one attempt, no retries, your request never blocks on a flag.

Batching, flush and shutdown

Events do not hit the network on every track(). They queue in memory and flush when the queue reaches flush_at (default 20), when flush_interval elapses on a long-running process, or when you say so:

$kilden->flush();   // blocking: drain everything queued right now
$kilden->close();   // flush with a 10s deadline, then refuse further events

Call close() at the end of CLI scripts and workers. Under FPM you can skip it: a register_shutdown_function hook flushes after the response is handed off. If the process dies before any flush path runs (kill -9, fatal at the wrong instant), queued events are lost — that is the documented trade-off of in-memory batching; anything stricter needs a persistent queue on your side.

The queue is bounded (max_queue_size, default 10 000). When full, the newest event is dropped and counted; $kilden->droppedCount() tells you how many events were lost to a full queue, invalid input or exhausted retries.

Options

$kilden = new Kilden\Client('sk_...', [
    'host'            => 'https://ingest.kilden.io',
    'flush_at'        => 20,
    'flush_interval'  => 10,
    'max_queue_size'  => 10000,
    'timeout'         => 3,
    'transport'       => null,     // autodetect: curl, then stream wrappers
    'debug'           => false,
    'enabled'         => true,     // false = full no-op for tests and local dev
]);

The constructor throws on misconfiguration (missing key, public key, no transport available) — fail at boot, not at 3am. After construction the SDK never throws: invalid input is dropped and logged, and delivery failures degrade to dropped batches, never to exceptions in your request path.

No ext-curl? The SDK falls back to stream wrappers automatically, and you can inject any Kilden\Transport\Transport implementation (that is how the WordPress plugin routes through wp_remote_post()).

Laravel

The kilden/laravel package wraps this SDK for Laravel 11–13: config file, Kilden facade, queued delivery, and the POST /kilden/identity endpoint the web SDK refreshes its tokens against.

// config/kilden.php via: php artisan vendor:publish --tag=kilden-config
Kilden::track($user->id, 'subscription_started', ['plan' => 'pro']);

// routes/web.php — one line, behind your auth middleware:
KildenRoutes::identity();

With KILDEN_QUEUE=true, event calls dispatch a Horizon/queue job instead of sending inline. Kilden::fake() gives you a spy with assertTracked() for your test suite.

Spec

This SDK implements the Kilden server SDK specification (spec version 0.1) and runs its frozen test vectors — including byte-exact identity token signatures — against the shared mock capture server in CI. Behavior changes land in the spec first, then here.

Community

License

MIT

kilden / kilden-php

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