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Checkout integration SDK

Paysera PHP SDK for integrating with the Paysera Checkout v3 API: payment initiation, callback verification, refunds, project eligibility, and localization — with a single SdkFacade entry point.

Supported PHP versions

PHP 7.4, 8.0, 8.1, 8.2, 8.3, and 8.4. The minimum requirement is declared in composer.json as ^7.4 || ^8.0.

Requirements

• PHP 7.4 or higher
• ext-curl
• ext-json
• ext-mbstring (optional — symfony/polyfill-mbstring is installed as a fallback)

Installation

Install via Composer:

Obtaining sandbox credentials

A sandbox project with API credentials is required to run the SDK end to end. Self-service onboarding for external integrators is documented on the Paysera developer portal at https://developers.paysera.com.

Code style

PSR-12. Built on top of PSR standards (PSR-3 logging, PSR-6 cache, PSR-18 HTTP client, PSR-20 clock).

Features

• JWT Token Validation: Automatic validation of JWT tokens with project ID extraction
• PSR-Compliant Caching: Configurable cache pool for improved performance
• Payment Processing: Full payment order creation and link generation
• Callback Processing: Secure webhook verification and processing
• Project Eligibility: Single-call eligibility check that combines payment-collection status and store-URL verification, with deterministic failed_to_check fallback for retry UX
• Translations: Namespace-based localization with SDK and plugin translation merging
• Multiple Environments: Support for both production and sandbox environments

Quick Start

SDK Facade Configuration

The SDK facade can be customized with various options:

JWKS cache

The SDK verifies JWT access token signatures against Keycloak's JWKS endpoint (/auth/realms/Paysera/protocol/openid-connect/certs). The key set is fetched once on cold start and cached for 30 days. The endpoint is re-contacted only when an incoming JWT carries a kid that is not present in the cached set (Keycloak key rotation).

To benefit from this strategy in production you must inject a persistent PSR-6 cache pool via setCacheItemPool(). The default InMemoryCache is scoped to a single PHP request and defeats the caching completely in shared-nothing deployments (PHP-FPM, multi-container setups), causing a /certs fetch on every validation.

Recommended backends: Redis, APCu, filesystem cache — anything that survives across PHP request lifecycles. Examples:

• Symfony: Symfony\Component\Cache\Adapter\RedisAdapter
• Laravel: Illuminate\Cache\Psr6\CachePool wrapping the application cache
• WordPress/WooCommerce: any plugin bridging WP transients or object cache to PSR-6
• Plain PHP: Symfony\Component\Cache\Adapter\FilesystemAdapter

If /certs is unreachable during a rotation fallback, JWT validation fails loudly — the SDK never accepts an unsigned or unverifiable token.

Forcing a JWKS refresh

Normal Keycloak rotation is handled automatically via the unknown-kid fallback. For incident response (revoked or compromised signing key), the cached key set must be purged from the PSR-6 pool so the next JWT validation cold-starts it from /certs again.

Firebase\JWT\CachedKeySet stores its entries under the jwks prefix, but setCacheKeys() SHA-256-hashes the composite key whenever it exceeds 64 characters — and every real Paysera JWKS URL crosses that threshold. The prefix is lost in the final storage key, which means a redis-cli --scan --pattern 'jwks*' sweep will not match anything.

The reliable approach is to dedicate an isolated PSR-6 pool to the SDK and clear it as a whole during an incident:

• Dedicated Redis DB: redis-cli -n <sdk-db-index> FLUSHDB
• Symfony Cache (dedicated pool): bin/console cache:pool:clear <paysera-sdk-pool>
• Dedicated filesystem cache: delete the cache directory (rm -rf var/cache/paysera-sdk/*) and reload the PHP-FPM pool
• APCu: apcu_clear_cache() only if APCu is not shared with unrelated application data; otherwise prefer a different backend

Sharing the SDK's PSR-6 pool with unrelated application caches defeats this procedure — a full flush would also wipe business data. Keep the pool SDK-scoped so incident response stays a one-liner.

HTTP client timeouts

JWKS fetches go through the PSR-18 client injected via setHttpClient() (or the default CurlHttpClient otherwise). During cold start and rotation fallback, the call blocks the caller thread. A slow or unreachable /certs endpoint with an unbounded client timeout turns every such call into a hung checkout request.

Required for production: configure a finite connect timeout (~5 s) and total-request timeout (~10 s) on the injected PSR-18 client.

• The default CurlHttpClient already sets CURLOPT_CONNECTTIMEOUT=10 and CURLOPT_TIMEOUT=30.
• Symfony HttpClient: HttpClient::create(['timeout' => 10, 'max_duration' => 10]).
• Guzzle: new Client(['connect_timeout' => 5, 'timeout' => 10]).

HTTP logging and redaction

Requests and responses are written to the PSR-3 logger passed to setLogger() through SecureApiClientFormatter. Nothing is logged at all while the default NullLogger is in place.

The formatter redacts sensitive query parameters, headers and body fields before the line is written. Body redaction is fail closed: a body is logged only when a body formatter claims its Content-Type. JSON (application/json and any +json subtype, including the application/problem+json of an RFC 7807 error) and application/x-www-form-urlencoded are handled out of the box, matched on the parsed media type — so parameters (; charset=utf-8), letter case and a header sent twice make no difference. Anything else — an unknown media type, or a response with no Content-Type header — is replaced with [UNSUPPORTED_CONTENT_TYPE], so an unrecognized payload never reaches the log.

Redacted by default: the query parameters and body fields client_id, client_secret, access_token, password and token, and the headers Authorization and Set-Cookie. Extend either list through the SecureApiClientFormatter constructor, and add handling for a further content type with addCustomBodyFormatter() — a custom formatter is consulted before the built-in ones, so it can also override how JSON or form-urlencoded bodies are redacted.

Exception context in logs

Internal SDK exceptions extend BaseException and carry diagnostic data that is not part of the exception message: which field failed validation, what the API actually answered. getContextData(): array returns that data as an array so a PSR-3 logger can render it.

It does not reach a log on its own. A PSR-3 normalizer resolves the standard Throwable fields — class, message, code, file, line, trace, previous — and calls no other getters, so render the context explicitly in your own normalizer, or pass it alongside the exception:

A public facade surfaces failures as IntegrationException, so the internal exception that carries the context is the one behind getPrevious().

getContext(): string is unchanged and still returns exactly what it returned before.

Two things to know before passing the array straight to a handler.

Only an array keyed entirely by strings is merged into the top level. Everything else — a list, an integer-keyed array, a scalar, a body that is not JSON — is appended as a list under the reserved key _raw, so read it from there rather than from the top level.

And the array holds the values as they were given, where getContext() flattened everything to a string at write time. An object passed to setContext() is therefore handed to your log formatter as an object, not as the flattened string getContext() produced — a formatter that recurses into it can write more than the string form ever did, and one that cannot encode it can fail on the whole record.

Documentation

Use Cases

• Authorization - Authenticate with the Payment API and decode JWT tokens
• Payment Initiation - Create payment orders and generate payment links
• Callback Processing - Securely process payment webhooks
• Project Eligibility - Check whether the current store is allowed to collect payments
• Merchant Area Deeplinks - Build project-specific Merchant Area URLs from the stored token
• Translations - Localization with SDK and plugin namespace support
• Payment Method Logos - Logo URLs provided by the API via PaymentMethod::getLogoUrl()
• Local Development - Setup and testing in development environment

Version History

See CHANGELOG.md for detailed version history and upgrade notes.

Contributing

See CONTRIBUTING.md. Paysera GitLab is the source of truth; the GitHub repository is a read-only mirror updated on every release tag.

Security

Vulnerabilities should be reported privately — see SECURITY.md. Please do not open public issues for security findings.

License

LGPL-3.0-or-later. The full license text is in LICENSE.