public function respondToAccessTokenRequest(
        ServerRequestInterface $request,
        ResponseTypeInterface $responseType,
        DateInterval $accessTokenTTL
    ) {
        // Validate request
        $client = $this->validateClient($request);
        $encryptedAuthCode = $this->getRequestParameter('code', $request, null);

        if ($encryptedAuthCode === null) {
            throw OAuthServerException::invalidRequest('code');
        }

        try {
            $authCodePayload = json_decode($this->decrypt($encryptedAuthCode));

            $this->validateAuthorizationCode($authCodePayload, $client, $request);

            $scopes = $this->scopeRepository->finalizeScopes(
                $this->validateScopes($authCodePayload->scopes),
                $this->getIdentifier(),
                $client,
                $authCodePayload->user_id
            );
        } catch (LogicException $e) {
            throw OAuthServerException::invalidRequest('code', 'Cannot decrypt the authorization code', $e);
        }

        // Validate code challenge
        if ($this->enableCodeExchangeProof === true) {
            $codeVerifier = $this->getRequestParameter('code_verifier', $request, null);

            if ($codeVerifier === null) {
                throw OAuthServerException::invalidRequest('code_verifier');
            }

            // Validate code_verifier according to RFC-7636
            // @see: https://tools.ietf.org/html/rfc7636#section-4.1
            if (preg_match('/^[A-Za-z0-9-._~]{43,128}$/', $codeVerifier) !== 1) {
                throw OAuthServerException::invalidRequest(
                    'code_verifier',
                    'Code Verifier must follow the specifications of RFC-7636.'
                );
            }

            switch ($authCodePayload->code_challenge_method) {
                case 'plain':
                    if (hash_equals($codeVerifier, $authCodePayload->code_challenge) === false) {
                        throw OAuthServerException::invalidGrant('Failed to verify `code_verifier`.');
                    }

                    break;
                case 'S256':
                    if (
                        hash_equals(
                            strtr(rtrim(base64_encode(hash('sha256', $codeVerifier, true)), '='), '+/', '-_'),
                            $authCodePayload->code_challenge
                        ) === false
                    ) {
                        throw OAuthServerException::invalidGrant('Failed to verify `code_verifier`.');
                    }
                    // @codeCoverageIgnoreStart
                    break;
                default:
                    throw OAuthServerException::serverError(
                        sprintf(
                            'Unsupported code challenge method `%s`',
                            $authCodePayload->code_challenge_method
                        )
                    );
                // @codeCoverageIgnoreEnd
            }
        }

        // Issue and persist new access token
        $accessToken = $this->issueAccessToken($accessTokenTTL, $client, $authCodePayload->user_id, $scopes);
        $this->getEmitter()->emit(new RequestEvent(RequestEvent::ACCESS_TOKEN_ISSUED, $request));
        $responseType->setAccessToken($accessToken);

        // Issue and persist new refresh token if given
        $refreshToken = $this->issueRefreshToken($accessToken);

        if ($refreshToken !== null) {
            $this->getEmitter()->emit(new RequestEvent(RequestEvent::REFRESH_TOKEN_ISSUED, $request));
            $responseType->setRefreshToken($refreshToken);
        }

        // Revoke used auth code
        $this->authCodeRepository->revokeAuthCode($authCodePayload->auth_code_id);

        return $responseType;
    }