packbackbooks/lti-1-3-php-library

<?php

namespace Packback\Lti1p3;

use Exception;
use Firebase\JWT\JWT;
use GuzzleHttp\Client;
use GuzzleHttp\Exception\ClientException;
use Packback\Lti1p3\Interfaces\ICache;
use Packback\Lti1p3\Interfaces\ILtiRegistration;
use Packback\Lti1p3\Interfaces\ILtiServiceConnector;
use Packback\Lti1p3\Interfaces\IServiceRequest;
use Psr\Http\Message\ResponseInterface;

class LtiServiceConnector implements ILtiServiceConnector
{
    public const NEXT_PAGE_REGEX = '/<([^>]*)>; ?rel="next"/i';
    private bool $debuggingMode = false;

    public function __construct(
        private ICache $cache,
        private Client $client
    ) {}

    public function setDebuggingMode(bool $enable): self
    {
        $this->debuggingMode = $enable;

        return $this;
    }

    public function getAccessToken(ILtiRegistration $registration, array $scopes): string
    {
        // Get a unique cache key for the access token
        $accessTokenKey = $this->getAccessTokenCacheKey($registration, $scopes);
        // Get access token from cache if it exists
        $accessToken = $this->cache->getAccessToken($accessTokenKey);

        if (isset($accessToken)) {
            return $accessToken;
        }

        // Build up JWT to exchange for an auth token
        $clientId = $registration->getClientId();
        $jwtClaim = [
            'iss' => $clientId,
            'sub' => $clientId,
            'aud' => $registration->getAuthServer(),
            'iat' => time() - 5,
            'exp' => time() + 60,
            'jti' => 'lti-service-token'.hash('sha256', random_bytes(64)),
        ];

        // Sign the JWT with our private key (given by the platform on registration)
        $jwt = JWT::encode($jwtClaim, $registration->getToolPrivateKey(), 'RS256', $registration->getKid());

        // Build auth token request headers
        $authRequest = [
            'grant_type' => 'client_credentials',
            'client_assertion_type' => 'urn:ietf:params:oauth:client-assertion-type:jwt-bearer',
            'client_assertion' => $jwt,
            'scope' => implode(' ', $scopes),
        ];

        // Get Access
        $request = new ServiceRequest(
            ServiceRequest::METHOD_POST,
            $registration->getAuthTokenUrl(),
            ServiceRequest::TYPE_AUTH
        );
        $request->setPayload(['form_params' => $authRequest])
            ->setMaskResponseLogs(true);
        $response = $this->makeRequest($request);

        $tokenData = $this->getResponseBody($response);

        // Cache access token
        $this->cache->cacheAccessToken($accessTokenKey, $tokenData['access_token']);

        return $tokenData['access_token'];
    }

    public function makeRequest(IServiceRequest $request): ResponseInterface
    {
        $response = $this->client->request(
            $request->getMethod(),
            $request->getUrl(),
            $request->getPayload()
        );

        if ($this->debuggingMode) {
            $this->logRequest(
                $request,
                $this->getResponseHeaders($response),
                $this->getResponseBody($response)
            );
        }

        return $response;
    }

    public function getResponseHeaders(ResponseInterface $response): ?array
    {
        $responseHeaders = $response->getHeaders();
        array_walk($responseHeaders, function (&$value) {
            $value = $value[0];
        });

        return $responseHeaders;
    }

    public function getResponseBody(ResponseInterface $response): ?array
    {
        $responseBody = (string) $response->getBody();

        return json_decode($responseBody, true);
    }

    public function makeServiceRequest(
        ILtiRegistration $registration,
        array $scopes,
        IServiceRequest $request,
        bool $shouldRetry = true
    ): array {
        $request->setAccessToken($this->getAccessToken($registration, $scopes));

        try {
            $response = $this->makeRequest($request);
        } catch (ClientException $e) {
            $status = $e->getResponse()->getStatusCode();

            // If the error was due to invalid authentication and the request
            // should be retried, clear the access token and retry it.
            if ($status === 401 && $shouldRetry) {
                $key = $this->getAccessTokenCacheKey($registration, $scopes);
                $this->cache->clearAccessToken($key);

                return $this->makeServiceRequest($registration, $scopes, $request, false);
            }

            throw $e;
        }

        return [
            'headers' => $this->getResponseHeaders($response),
            'body' => $this->getResponseBody($response),
            'status' => $response->getStatusCode(),
        ];
    }

    public function getAll(
        ILtiRegistration $registration,
        array $scopes,
        IServiceRequest $request,
        ?string $key = null
    ): array {
        if ($request->getMethod() !== ServiceRequest::METHOD_GET) {
            throw new Exception('An invalid method was specified by an LTI service requesting all items.');
        }

        $results = [];
        $nextUrl = $request->getUrl();

        while ($nextUrl) {
            $request->setUrl($nextUrl);
            $response = $this->makeServiceRequest($registration, $scopes, $request);
            $pageResults = $this->getResultsFromResponse($response, $key);
            $results = array_merge($results, $pageResults);
            $nextUrl = $this->getNextUrl($response['headers']);
        }

        return $results;
    }

    public static function getLogMessage(
        IServiceRequest $request,
        array $responseHeaders,
        ?array $responseBody
    ): string {
        if ($request->getMaskResponseLogs()) {
            $responseHeaders = self::maskValues($responseHeaders);
            $responseBody = self::maskValues($responseBody);
        }

        $contextArray = [
            'request_method' => $request->getMethod(),
            'request_url' => $request->getUrl(),
            'response_headers' => $responseHeaders,
            'response_body' => $responseBody,
        ];

        $requestBody = $request->getPayload()['body'] ?? null;

        if (isset($requestBody)) {
            $contextArray['request_body'] = $requestBody;
        }

        return implode(' ', array_filter([
            $request->getErrorPrefix(),
            json_decode($requestBody)->userId ?? null,
            json_encode($contextArray),
        ]));
    }

    private function logRequest(
        IServiceRequest $request,
        array $responseHeaders,
        ?array $responseBody
    ): void {
        error_log(self::getLogMessage($request, $responseHeaders, $responseBody));
    }

    private static function maskValues(?array $payload): ?array
    {
        if (!isset($payload) || empty($payload)) {
            return $payload;
        }

        foreach ($payload as $key => $value) {
            $payload[$key] = '***';
        }

        return $payload;
    }

    private function getAccessTokenCacheKey(ILtiRegistration $registration, array $scopes): string
    {
        sort($scopes);
        $scopeKey = md5(implode('|', $scopes));

        return $registration->getIssuer().$registration->getClientId().$scopeKey;
    }

    private function getResultsFromResponse(array $response, ?string $key = null): array
    {
        if (isset($key)) {
            return $response['body'][$key] ?? [];
        }

        return $response['body'] ?? [];
    }

    private function getNextUrl(array $headers): ?string
    {
        $subject = $headers['Link'] ?? $headers['link'] ?? '';
        preg_match(static::NEXT_PAGE_REGEX, $subject, $matches);

        return $matches[1] ?? null;
    }
}