Whoops, looks like something went wrong.

        if ($site === null || $language === null) {
            return self::CALLBACK_SLUG;
        }

        $siteConfiguration = $site->getConfiguration();
        $languageConfiguration = $language->toArray();
        $callbackSlug = empty($languageConfiguration['oauth2_callback_slug'])
                              ? ($siteConfiguration['oauth2_callback_slug'] ?? '')
                              : ($languageConfiguration['oauth2_callback_slug']);

    {
        return sprintf(
            '%s/%s',
            $this->getBaseUri($request),
            $this->buildCallbackSlug($request)
        );
    }

    private function buildCallbackSlug(ServerRequestInterface $request = null): string

    public function doesTheRemoteInstanceCallUsBack(ServerRequestInterface $request = null): bool
    {
        $request = $this->getRequest($request);
        $callbackUri = new Uri($this->buildCallbackBaseUri($request));
        return trim($request->getUri()->getPath(), '/') === trim($callbackUri->getPath(), '/');
    }

    public function getBaseUri(ServerRequestInterface $request = null): string

        // TYPO3\CMS\Frontend\Authentication\FrontendUserAuthentication->formfield_status
        $loginControllerIsRequested = ($mergedRequestedParameters['logintype'] ?? null) === 'login' || $this->requestStates->isCurrentController(RequestStates::CONTROLLER_LOGIN, $request);
        $registrationControllerIsRequested = ($getParameters['tx_oauth2client']['action'] ?? null) === 'authorize' || ($getParameters['tx_oauth2client']['action'] ?? null) === 'verify';
        $theRemoteInstanceCallsUsBack = $this->siteService->doesTheRemoteInstanceCallUsBack($request);
        $oauth2FlowIsDone = $this->requestStates->isCurrentAction(RequestStates::ACTION_LOGIN_DONE, $request);

        if ($loginControllerIsRequested && $oauth2FlowIsDone && !$registrationControllerIsRequested) {
            // we are here because of a sub-request from AfterAuthenticationHandler

                if (!$middleware instanceof MiddlewareInterface) {
                    throw new \InvalidArgumentException(get_class($middleware) . ' does not implement ' . MiddlewareInterface::class, 1516821342);
                }
                return $middleware->process($request, $this->next);
            }
        };
    }
}

        ) {
            return GeneralUtility::makeInstance(ErrorController::class)->unavailableAction($request, 'This page is temporarily unavailable.');
        }
        // Continue the regular stack if no maintenance mode is active
        return $handler->handle($request);
    }
}

                if (!$middleware instanceof MiddlewareInterface) {
                    throw new \InvalidArgumentException(get_class($middleware) . ' does not implement ' . MiddlewareInterface::class, 1516821342);
                }
                return $middleware->process($request, $this->next);
            }
        };
    }
}

        $request = $request->withAttribute('routing', $routeResult);
        if ($routeResult->getLanguage() instanceof SiteLanguage) {
            Locales::setSystemLocaleFromSiteLanguage($routeResult->getLanguage());
        }
        return $handler->handle($request);
    }
}

                if (!$middleware instanceof MiddlewareInterface) {
                    throw new \InvalidArgumentException(get_class($middleware) . ' does not implement ' . MiddlewareInterface::class, 1516821342);
                }
                return $middleware->process($request, $this->next);
            }
        };
    }
}

    {
        $eID = $request->getParsedBody()['eID'] ?? $request->getQueryParams()['eID'] ?? null;

        if ($eID === null) {
            return $handler->handle($request);
        }

        // Remove any output produced until now
        ob_clean();

                if (!$middleware instanceof MiddlewareInterface) {
                    throw new \InvalidArgumentException(get_class($middleware) . ' does not implement ' . MiddlewareInterface::class, 1516821342);
                }
                return $middleware->process($request, $this->next);
            }
        };
    }
}

     */
    public function process(ServerRequestInterface $request, RequestHandlerInterface $handler): ResponseInterface
    {
        $request = $request->withAttribute('normalizedParams', NormalizedParams::createFromRequest($request));
        return $handler->handle($request);
    }
}

                if (!$middleware instanceof MiddlewareInterface) {
                    throw new \InvalidArgumentException(get_class($middleware) . ' does not implement ' . MiddlewareInterface::class, 1516821342);
                }
                return $middleware->process($request, $this->next);
            }
        };
    }
}

                1396795884
            );
        }

        return $handler->handle($request);
    }

    /**
     * Checks if the provided host header value matches the trusted hosts pattern.

                if (!$middleware instanceof MiddlewareInterface) {
                    throw new \InvalidArgumentException(get_class($middleware) . ' does not implement ' . MiddlewareInterface::class, 1516821342);
                }
                return $middleware->process($request, $this->next);
            }
        };
    }
}

        $this->timeTracker->setEnabled($timeTrackingEnabled);
        $this->timeTracker->start(microtime(true));
        $this->timeTracker->push('');

        $response = $handler->handle($request);

        // Finish time tracking
        $this->timeTracker->pull();
        $this->timeTracker->finish();

                if (!$middleware instanceof MiddlewareInterface) {
                    throw new \InvalidArgumentException(get_class($middleware) . ' does not implement ' . MiddlewareInterface::class, 1516821342);
                }
                return $middleware->process($request, $this->next);
            }
        };
    }
}

     * Invoke the middleware stack
     */
    public function handle(ServerRequestInterface $request): ResponseInterface
    {
        return $this->tip->handle($request);
    }

    /**
     * Seed the middleware stack with the inner request handler

    public function handle(ServerRequestInterface $request): ResponseInterface
    {
        try {
            $response = $this->requestHandler->handle($request);
        } catch (ImmediateResponseException $exception) {
            $response = $exception->getResponse();
        }
        return $response;

        // Create new request object having applicationType "I am a frontend request" attribute.
        $request = $request->withAttribute('applicationType', SystemEnvironmentBuilder::REQUESTTYPE_FE);

        $this->initializeContext();
        return parent::handle($request);
    }

    /**
     * Create a PSR-7 Response that redirects to the install tool

     * Set up the application and shut it down afterwards
     */
    final public function run()
    {
        $response = $this->handle(ServerRequestFactory::fromGlobals());
        $this->sendResponse($response);
    }
}

// Set up the application for the frontend
call_user_func(static function () {
    $classLoader = require dirname(__DIR__).'/vendor/autoload.php';
    \TYPO3\CMS\Core\Core\SystemEnvironmentBuilder::run(0, \TYPO3\CMS\Core\Core\SystemEnvironmentBuilder::REQUESTTYPE_FE);
    \TYPO3\CMS\Core\Core\Bootstrap::init($classLoader)->get(\TYPO3\CMS\Frontend\Http\Application::class)->run();
});

call_user_func(static function () {
    $classLoader = require dirname(__DIR__).'/vendor/autoload.php';
    \TYPO3\CMS\Core\Core\SystemEnvironmentBuilder::run(0, \TYPO3\CMS\Core\Core\SystemEnvironmentBuilder::REQUESTTYPE_FE);
    \TYPO3\CMS\Core\Core\Bootstrap::init($classLoader)->get(\TYPO3\CMS\Frontend\Http\Application::class)->run();
});