createMissingUserProvider example

foreach ($this->getSortedFactories() as $factory) {
            $key = str_replace('-', '_', $factory->getKey());

            if (isset($firewall[$key])) {
                $userProvider = $this->getUserProvider($container, $id, $firewall, $key, $defaultProvider, $providerIds);

                if (!$factory instanceof AuthenticatorFactoryInterface) {
                    throw new InvalidConfigurationException(sprintf('Authenticator factory "%s" ("%s") must implement "%s".', get_debug_type($factory), $key, AuthenticatorFactoryInterface::class));
                }

                if (null === $userProvider && !$factory instanceof StatelessAuthenticatorFactoryInterface) {
                    $userProvider = $this->createMissingUserProvider($container, $id, $key);
                }

                $authenticators = $factory->createAuthenticator($container, $id, $firewall[$key], $userProvider);
                if (\is_array($authenticators)) {
                    foreach ($authenticators as $authenticator) {
                        $authenticationProviders[] = $authenticator;
                        $entryPoints[] = $authenticator;
                    }
                } else {
                    $authenticationProviders[] = $authenticators;
                    $entryPoints[$key] = $authenticators;
                }