README

Comfino PHP API client

Comfino PHP API client library

A portable, PSR-compliant PHP protocol layer for the Comfino payment gateway REST API. This library handles all HTTP communication with the Comfino API: creating and managing loan applications (orders), querying available financial products, verifying webhook signatures, and generating paywall iframe authentication tokens for the shop checkout page. It imposes no concrete HTTP client, serializer, or framework dependency — bring your own PSR-18 client and PSR-17 factories.

Features

PSR-18 HTTP Client / PSR-7 Messages / PSR-17 Factories support.
Production and sandbox environment support.
Exponential backoff retry for transient API errors.
Secure webhook handling with CR-Signature (SHA3-256) verification.
Time-limited HMAC-signed auth token generation for paywall iframe embedded at the shop checkout page.
Typed exception hierarchy mapped to HTTP status codes.
Forward-compatible enums: unknown API values are represented as flyweights rather than thrown as errors.

Requirements

PHP 8.1 or higher
Extensions: ext-json, ext-sodium, ext-zlib
PSR-18 HTTP Client and PSR-17 HTTP Factories implementations
Composer

Installation

composer require comfino/php-api-client

Suggested companion packages:

composer require nyholm/psr7               # PSR-7/17 message and factory implementation
composer require sunrise/http-client-curl  # PSR-18 cURL client implementation

Quick start

The API key is issued by Comfino when your shop signs a merchant contract. It authenticates all server-to-server API calls and must be kept secret — never expose it in frontend code, browser requests, or public repositories.

use Comfino\Api\Client;
use Nyholm\Psr7\Factory\Psr17Factory;
use Sunrise\Http\Client\Curl\Client as CurlClient;

$psr17Factory = new Psr17Factory();

$client = new Client(
    httpClient: new CurlClient($psr17Factory),
    requestFactory: $psr17Factory,
    streamFactory: $psr17Factory,
    apiKey: 'your-api-key' // Private - keep server-side only.
);

$client->enableSandboxMode(); // Omit or call disableSandboxMode() for production.

// Submit a loan application.
$response = $client->createOrder($order); // $order implements OrderInterface
header('Location: ' . $response->applicationUrl);

Usage

Client configuration

// Override the default user agent.
$client->setCustomUserAgent('my-plugin/1.0.0');

// Set the API language (ISO 639-1) and currency (ISO 4217).
$client->setApiLanguage('pl');
$client->setApiCurrency('PLN');

// Add a custom HTTP header (e.g., for platform identification).
$client->addCustomHeader('X-Shop-Platform', 'WooCommerce/8.5');

// Use a different API endpoint (e.g., staging).
$client->setCustomApiBaseUrl('https://staging-api.example.com');

Querying financial products

use Comfino\Api\Dto\Payment\LoanQueryCriteria;
use Comfino\Enum\LoanType;
use Comfino\Enum\ProductListType;

// List all products for a 1 500 PLN cart (amounts in grosz).
$criteria = new LoanQueryCriteria(loanAmount: 150000);
$response = $client->getFinancialProducts($criteria);

foreach ($response->financialProducts as $product) {
    echo $product->name . ' - ' . $product->instalmentAmount . " grosz/month\n";
}

// Filter by product type.
$criteria = new LoanQueryCriteria(
    loanAmount: 150000,
    loanType: LoanType::INSTALLMENTS_ZERO_PERCENT
);

// Get detailed information about a specific financial product (e.g., for a product detail page).
$details = $client->getFinancialProductDetails($criteria, $cart); // $cart implements CartInterface

// Get available product types configured for this shop account (for promotional banner widget at shop product page).
$types = $client->getProductTypes(ProductListType::WIDGET);

Order management

// Create a loan application - $order implements Comfino\Shop\Order\OrderInterface.
$createResponse = $client->createOrder($order);
$applicationUrl = $createResponse->applicationUrl;

// Validate an order without submitting it.
$validateResponse = $client->validateOrder($order);

// Cancel an order.
$client->cancelOrder('ORDER-123');

See request-signing.md for details on how request signatures are computed automatically for order creation.

Account and widget

The widget key is a public identifier associated with the Comfino merchant account pointed to by the API key. Unlike the API key, it is safe to embed in frontend scripts — it is used by the Comfino Web Frontend SDK to render the promotional banner widget and the paywall iframe at the shop checkout page.

// Check that the API key belongs to an active account.
$isActive = $client->isShopAccountActive();

// Retrieve the widget key (public) for use in frontend scripts (e.g., promotional banner).
$widgetKey = $client->getWidgetKey();

// List available widget types.
$widgetTypes = $client->getWidgetTypes();

Notifications (fire-and-forget)

These methods catch all exceptions internally and return bool. They are safe to call without a try/catch block.

use Comfino\Api\Dto\Plugin\ShopPluginError;

// Report a plugin error for remote diagnostics (e.g., from an exception handler).
$client->sendLoggedError(new ShopPluginError(
    host: 'myshop.example.com',
    platform: 'ExampleEcommercePlatform',
    environment: ['php' => PHP_VERSION, 'plugin' => '2.0.0'],
    errorCode: 'API_ERROR',
    errorMessage: 'Unexpected API response.',
    stackTrace: $exception->getTraceAsString()
));

// Notify Comfino when the payment plugin is uninstalled.
$client->notifyPluginRemoval();

// Notify Comfino of an abandoned cart event.
$client->notifyAbandonedCart('checkout_abandoned');

Webhook signature verification

Comfino signs status-update webhook requests with a CR-Signature header. Verify it before processing:

use Comfino\Auth\WebhookSignatureVerifier;

$verifier = new WebhookSignatureVerifier();

$signature = $_SERVER['HTTP_CR_SIGNATURE'] ?? '';
$payload = file_get_contents('php://input');

if (!$verifier->verify($signature, 'your-api-key', $payload)) {
    http_response_code(401);
    exit;
}

// Process verified payload.
$data = json_decode($payload, true);

See webhook-verification.md for comprehensive webhook handling patterns, including framework integration, multiple API keys, replay attack prevention, and troubleshooting.

Paywall authentication token

The Comfino paywall iframe embedded at the shop checkout page requires a short-lived signed token. Generate one server-side per page render using the public widget key and the private API key, then pass only the resulting token to the frontend — the API key never leaves the server:

use Comfino\Auth\PaywallAuthKeyGenerator;

$generator = new PaywallAuthKeyGenerator();
// $widgetKey - public, obtained via $client->getWidgetKey() and stored in shop config
// $apiKey - private, never sent to the browser
$authKey = $generator->generateAuthKey(widgetKey: $widgetKey, apiKey: $apiKey);

// Pass only $authKey to the frontend widget initialization script served from the Comfino CDN (part of the official Comfino Web Frontend SDK).

Tokens are valid for 15 minutes (enforced server-side).

Serving many merchants from one process

Comfino\Api\Client holds one merchant's credentials as mutable state, which is right for a shop plugin and wrong for a long-lived service that handles many merchants in sequence. For that, use SharedClient: it stores no credential at all, so a single instance — one transport, one connection pool, one retry executor — can serve every tenant.

use Comfino\Api\ApiContext;
use Comfino\Api\RequestOptions;
use Comfino\Api\SharedClient;

// Register this once, as a service. It is stateless and safe to share.
$client = new SharedClient(
    httpClient: $httpClient,
    requestFactory: $requestFactory,
    streamFactory: $streamFactory,
    retryExecutor: new RetryExecutor($retryPolicy)
);

// Build one context per merchant, per request. Immutable, so it cannot be mutated out from under a call.
$context = new ApiContext(
    apiKey: $merchant->apiKey,
    sandboxMode: $merchant->isSandbox,
    tenantKey: $merchant->id // Partitions the limiter, the breaker, and your own metrics.
);

$products = $client->getFinancialProducts($context, $criteria, RequestOptions::attempts(2));
$order = $client->createOrder($context, $order, RequestOptions::failFast());

Keep the PSR-18 transport shared. The credential is a header, not a connection property, so one TLS pool serving every tenant is both safe and the point — giving each merchant its own transport costs a handshake per merchant per request.

Already have code written against the mutable surface? SharedClient::bind($context) returns a BoundClient implementing the same ClientInterface, one binding per tenant, with the credential still off anything shared.

Retry, backoff and timeout escalation

Wrap the client with a RetryExecutor to retry transient failures with exponentially growing, jittered delays:

use Comfino\Api\Client;
use Comfino\Api\Retry\ExponentialBackoffRetryPolicy;
use Comfino\Api\Retry\RetryExecutor;
use Comfino\Api\Retry\TimeoutConfig;

$retryPolicy = new ExponentialBackoffRetryPolicy(
    timeoutConfig: new TimeoutConfig(connectionTimeout: 5, transferTimeout: 15),
    maxAttempts: 3,
    maxTotalTransferTimeout: 15, // Budget shared by every attempt; null restores unbounded escalation.
    baseDelayMs: 100, // 0 disables the delay entirely
    maxDelayMs: 2000
);

$client = new Client(
    httpClient: $httpClient,
    requestFactory: $requestFactory,
    streamFactory: $streamFactory,
    apiKey: 'your-api-key',
    retryExecutor: new RetryExecutor($retryPolicy)
);

Two schedules grow per attempt, and they answer different failures. The timeout doubles, which is the right answer to a slow far side. The delay doubles with full jitter, which is the right answer to a refused connection — and to not turning every tenant on a node into one synchronized retry wave. Both are bounded: the escalation by maxTotalTransferTimeout, the delay by maxDelayMs. They bound different clocks, so getWorstCaseWallClockMs() reports the sum, which is the number to size a request latency budget against.

On a path that cannot absorb a sleep, say so rather than sleeping in it:

// One attempt, no delay: surface the failure and let the shopper pick another method.
$policy = ExponentialBackoffRetryPolicy::failFast(new TimeoutConfig(1, 3));

// Retries, but never sleeping.
$policy = ExponentialBackoffRetryPolicy::withoutDelay(new TimeoutConfig(1, 3), maxAttempts: 2);

Retryable failures are transport errors, HTTP 429, 502, 503 and 504, plus 500 for requests that are safe to replay. A Retry-After header is honored in both of its RFC 9110 forms and clamped, so a wrong header cannot park a worker.

Order creation is safe to retry and needs no idempotency key. The API deduplicates a replayed POST /orders by orderId — mandatory, and unique per shop — plus the hash of the request body: a request for an id that already exists with the same body is answered with the existing order at 201 Created rather than creating a second loan application, and a differing body under the same id is rejected as a validation error. The one thing this asks of a caller is not to vary the body between attempts; the client builds each request once and reuses it across attempts, so that holds automatically.

If you write a Request of your own against an endpoint with no such key, say so and it will be sent exactly once:

final class RegisterSomething extends Request
{
    public function isIdempotent(): bool
    {
        return false; // No dedup key server-side, so never replay it.
    }

    // ...
}

For per-request timeouts to reach the wire, the transport has to accept them. Implement TimeoutConfigurableClientInterface::withTimeouts(), which returns a configured copy, or wrap a transport whose timeouts are construction options:

use Comfino\Api\Retry\CallbackTimeoutAwareClient;
use Comfino\Api\Retry\TimeoutConfig;
use Symfony\Component\HttpClient\Psr18Client;

$transport = new CallbackTimeoutAwareClient(
    fn (TimeoutConfig $t) => new Psr18Client(
        $symfonyHttpClient->withOptions(['timeout' => $t->connectionTimeout, 'max_duration' => $t->transferTimeout])
    ),
    new TimeoutConfig(connectionTimeout: 1, transferTimeout: 3)
);

The older TimeoutAwareClientInterface::updateTimeouts() is still honored, but it mutates the transport in place and never restores it — on transport shared between tenants, one tenant's escalated budget stays applied to the next tenant's call. Prefer the copy-returning interface.

Circuit breaker and outbound rate limiting

Both are optional and off by default. A breaker stops a Comfino outage from becoming your outage: instead of every worker paying the full timeout on a dead socket, calls fail immediately once a host looks unhealthy.

use Comfino\Api\CircuitBreaker\CircuitBreaker;
use Comfino\Api\RateLimit\TokenBucketRateLimiter;
use Comfino\Api\RateLimit\TwoTierRateLimiter;

$client = new SharedClient(
    httpClient: $httpClient,
    requestFactory: $requestFactory,
    streamFactory: $streamFactory,
    retryExecutor: new RetryExecutor($retryPolicy),
    rateLimiter: new TwoTierRateLimiter(
        perTenantLimiter: new TokenBucketRateLimiter(capacity: 20, refillTokensPerSecond: 5),
        globalLimiter: new TokenBucketRateLimiter(capacity: 200, refillTokensPerSecond: 50)
    ),
    circuitBreaker: new CircuitBreaker()
);

The breaker is keyed by (tenantKey, host), and only transport failures and 5xx feed it: one merchant's wrong API key produces 401s, and a breaker opened by those would block every healthy merchant on the same host. The limiter is non-blocking by contract — what happens on rejection is a call-site decision:

use Comfino\Api\OnLimit;

// Checkout: surface ServiceUnavailable and let the shopper choose another method.
$client->getFinancialProducts($context, $criteria, (new RequestOptions())->andOnLimit(OnLimit::FailFast));

// Worker: catch RateLimitExceeded, read getRetryAfterMs(), and put the call back on your queue.
$client->cancelOrder($context, $orderId, (new RequestOptions())->andOnLimit(OnLimit::Queue));

Pass a shared store to either one (both take a store interface) when several workers need to agree on what they have learned; the in-memory defaults are per process.

Observing requests and retries

Implement RequestObserverInterface or RetryObserverInterface to emit per-tenant metrics without patching anything. Both receive the tenant, so nothing has to be inferred:

final class MetricsObserver implements RequestObserverInterface
{
    public function onResponse(ApiContext $c, RequestInterface $rq, ResponseInterface $rs, float $durationMs): void
    {
        $this->histogram->observe($durationMs, ['tenant' => $c->tenantKey, 'status' => $rs->getStatusCode()]);
    }

    // onRequest() and onFailure() omitted for brevity.
}

Custom requests

Call an endpoint that doesn't have a dedicated client method yet with sendCustomRequest(). It reuses the same authentication, track ID, and error-mapping infrastructure as every built-in method:

use Comfino\Api\Request\CustomRequest;

// Free-form JSON in, free-form JSON out - no Request/Response subclass needed.
$response = $client->sendCustomRequest(
    new CustomRequest(method: 'POST', endpointPath: 'orders/ORDER-123/notes', body: ['note' => 'Called back, will retry payment.'])
);

$response->body; // Deserialized response body, verbatim (array|string|bool|int|float|null)

For a typed response, pass your own Response subclass (see src/Api/Response/GetProductTypes.php for a minimal example) as the second argument:

$response = $client->sendCustomRequest(new CustomRequest('GET', 'orders/ORDER-123/notes'), MyNotesResponse::class);

Error handling

All API errors are thrown as typed exceptions that implement HttpErrorExceptionInterface and preserve the original request and response bodies for debugging:

HTTP status	Exception	Description
400	`Comfino\Api\Exception\RequestValidationError`	Invalid request data.
401	`Comfino\Api\Exception\AuthorizationError`	Missing or invalid API key.
403	`Comfino\Api\Exception\Forbidden`	Permission issues.
404	`Comfino\Api\Exception\NotFound`	Resource not found.
405	`Comfino\Api\Exception\MethodNotAllowed`	HTTP method not allowed.
409	`Comfino\Api\Exception\Conflict`	Resource state conflict.
5xx	`Comfino\Api\Exception\ServiceUnavailable`	Server-side error.
timeout/retry exhausted	`Comfino\Api\Exception\ConnectionTimeout`	HTTP client timeout or all retry attempts failed.

use Comfino\Api\Exception\AuthorizationError;
use Comfino\Api\Exception\RequestValidationError;
use Comfino\Api\Exception\ServiceUnavailable;

try {
    $response = $client->createOrder($order);
} catch (RequestValidationError $e) {
    // $e->errors contains field-level validation messages from the API.
} catch (AuthorizationError $e) {
    // Invalid or missing API key.
} catch (ServiceUnavailable $e) {
    // Comfino API is temporarily unavailable.
}

Development

The bin/ wrappers delegate to Docker containers when docker-compose is available, or fall back to the host PHP. Two containers are used:

php-api-client — standard container, no Xdebug. Start it once with docker-compose up -d.
php-api-client-coverage — built with Xdebug (XDEBUG_MODE=coverage). Started on demand automatically by bin/phpunit whenever a --coverage* flag is detected; no manual up needed.

# Start the standard development container.
docker-compose up -d

# Install dependencies.
./bin/composer install

# Run all tests.
./bin/composer test

# Run unit tests only.
./bin/phpunit --testsuite Unit

# Run integration tests against the sandbox (requires a sandbox API key).
COMFINO_SANDBOX_API_KEY=your-key ./bin/phpunit --testsuite Integration

# Generate HTML coverage report (Xdebug container starts automatically).
./bin/phpunit --coverage-html coverage

# Check PSR-12 code style.
./bin/composer cs

# Auto-fix PSR-12 violations.
./bin/composer cs-fix

# Run PHPStan static analysis (level 6).
./bin/composer analyse

PSR standards

PSR-4 autoloading
PSR-7 HTTP messages
PSR-17 HTTP factories
PSR-18 HTTP client
PSR-12 coding style

Changelog

See CHANGELOG for recent changes.

License

BSD 3-Clause License. See LICENSE for details.

Support

Bug reports and feature requests: GitHub issue tracker.

Contributing

The GitHub repository is a read-only public mirror that receives automated clean-snapshot releases. Please report bugs and suggest improvements via the issue tracker.

comfino / php-api-client

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