# OPAClient.java

    /*
     *  Copyright (c) 2022, WSO2 Inc. (http://www.wso2.org) All Rights Reserved.
     *
     *  WSO2 Inc. licenses this file to you under the Apache License,
     *  Version 2.0 (the "License"); you may not use this file except
     *  in compliance with the License.
     *  You may obtain a copy of the License at
     *
     *    http://www.apache.org/licenses/LICENSE-2.0
     *
     *  Unless required by applicable law or agreed to in writing,
     *  software distributed under the License is distributed on an
     *  "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
     *  KIND, either express or implied.  See the License for the
     *  specific language governing permissions and limitations
     *  under the License.
     */

    package org.apache.synapse.mediators.opa;

    import org.apache.commons.httpclient.HttpStatus;
    import org.apache.commons.logging.Log;
    import org.apache.commons.logging.LogFactory;
    import org.apache.http.HttpEntity;
    import org.apache.http.client.config.RequestConfig;
    import org.apache.http.client.methods.CloseableHttpResponse;
    import org.apache.http.client.methods.HttpPost;
    import org.apache.http.config.Registry;
    import org.apache.http.config.RegistryBuilder;
    import org.apache.http.conn.socket.ConnectionSocketFactory;
    import org.apache.http.conn.ssl.SSLConnectionSocketFactory;
    import org.apache.http.conn.ssl.SSLContexts;
    import org.apache.http.conn.ssl.X509HostnameVerifier;
    import org.apache.http.entity.ContentType;
    import org.apache.http.entity.StringEntity;
    import org.apache.http.impl.client.CloseableHttpClient;
    import org.apache.http.impl.client.HttpClients;
    import org.apache.http.impl.conn.PoolingHttpClientConnectionManager;

    import java.io.BufferedReader;
    import java.io.File;
    import java.io.FileInputStream;
    import java.io.IOException;
    import java.io.InputStream;
    import java.io.InputStreamReader;
    import java.net.MalformedURLException;
    import java.net.URL;
    import java.nio.charset.Charset;
    import java.nio.charset.StandardCharsets;
    import java.security.KeyManagementException;
    import java.security.KeyStore;
    import java.security.KeyStoreException;
    import java.security.NoSuchAlgorithmException;
    import java.security.cert.CertificateException;
    import java.util.Map;

    import javax.net.ssl.SSLContext;

    /**
     * This class represents the client used to request and retrieve OPA response for a given policy
     * from the OPA server
     */
    public class OPAClient {

        private static final Log log = LogFactory.getLog(OPAClient.class);

        private int maxOpenConnections = 500;
        private int maxPerRoute = 200;
        private int connectionTimeout = 30;

        private CloseableHttpClient httpClient = null;

        public OPAClient(String url, Map<String, String> additionalParameters) throws OPASecurityException {

            if (additionalParameters.get(OPAConstants.MAX_OPEN_CONNECTIONS_PARAMETER) != null) {
                this.maxOpenConnections =
                        Integer.parseInt(additionalParameters.get(OPAConstants.MAX_OPEN_CONNECTIONS_PARAMETER));
            }
            if (additionalParameters.get(OPAConstants.MAX_PER_ROUTE_PARAMETER) != null) {
                this.maxPerRoute = Integer.parseInt(additionalParameters.get(OPAConstants.MAX_PER_ROUTE_PARAMETER));
            }
            if (additionalParameters.get(OPAConstants.CONNECTION_TIMEOUT_PARAMETER) != null) {
                this.connectionTimeout =
                        Integer.parseInt(additionalParameters.get(OPAConstants.CONNECTION_TIMEOUT_PARAMETER));
            }
            httpClient = createHttpClient(url);
        }

        /**
         * Method to publish the OPA payload to the OPA server
         *
         * @param opaServerUrl The url of the opa server
         * @param payload      The payload of the request
         * @param credentials  Access key of the opa validation request
         * @return opa response String
         * @throws OPASecurityException
         */
        public String publish(String opaServerUrl, String payload, String credentials)
                throws OPASecurityException {

            if (log.isDebugEnabled()) {
                log.debug("Initializing opa policy validation request: [validation-endpoint] " + opaServerUrl);
            }

            HttpPost httpPost = new HttpPost(opaServerUrl);
            httpPost.setHeader(OPAConstants.CONTENT_TYPE_HEADER, OPAConstants.APPLICATION_JSON);
            if (credentials != null) {
                httpPost.setHeader(OPAConstants.AUTHORIZATION_HEADER, credentials);
            }
            CloseableHttpResponse response = null;
            try {
                httpPost.setEntity(new StringEntity(payload));
                response = httpClient.execute(httpPost);
                return extractResponse(response);
            } catch (IOException e) {
                log.error("Error occurred while publishing to OPA server", e);
                throw new OPASecurityException(OPASecurityException.INTERNAL_ERROR,
                        OPASecurityException.INTERNAL_ERROR_MESSAGE, e);
            } finally {
                httpPost.releaseConnection();
                if (response != null) {
                    try {
                        response.close();
                    } catch (IOException e) {
                        log.error("Error when closing the response of the opa request", e);
                    }
                }
            }
        }

        /**
         * Extract the opa response string from HTTP response
         *
         * @param response CloseableHttpResponse object
         * @return opaResponse String
         * @throws OPASecurityException
         */
        private String extractResponse(CloseableHttpResponse response)
                throws OPASecurityException {

            String opaResponse = null;
            try {
                int responseCode = response.getStatusLine().getStatusCode();
                if (responseCode != HttpStatus.SC_OK) {
                    log.error("Error occurred while connecting to the OPA server. " + responseCode + " response returned");
                    throw new OPASecurityException(OPASecurityException.INTERNAL_ERROR,
                            "Error while accessing the OPA server URL. " + response.getStatusLine());
                } else {
                    HttpEntity entity = response.getEntity();
                    Charset charset = ContentType.getOrDefault(entity).getCharset();
                    if (charset == null) {
                        charset = StandardCharsets.UTF_8;
                    }

                    BufferedReader reader = new BufferedReader(new InputStreamReader(entity.getContent(), charset));
                    String inputLine;
                    StringBuilder stringBuilder = new StringBuilder();

                    while ((inputLine = reader.readLine()) != null) {
                        stringBuilder.append(inputLine);
                    }
                    opaResponse = stringBuilder.toString();
                    if (log.isDebugEnabled()) {
                        log.debug("Response: [status-code] " + responseCode + " [message] " + opaResponse);
                    }
                }
            } catch (IOException e) {
                log.error("Error while reading the OPA policy validation response", e);
                throw new OPASecurityException(OPASecurityException.INTERNAL_ERROR,
                        "Error while reading the OPA policy validation response", e);
            }

            return opaResponse;
        }

        /**
         * Return a PoolingHttpClientConnectionManager instance
         *
         * @param protocol- service endpoint protocol. It can be http/https
         * @return PoolManager
         * @throws OPASecurityException
         */
        private PoolingHttpClientConnectionManager getPoolingHttpClientConnectionManager(String protocol)
                throws OPASecurityException {

            PoolingHttpClientConnectionManager poolManager;
            if (OPAConstants.HTTPS.equals(protocol)) {

                char[] trustStorePassword =
                        System.getProperty(OPAConstants.TRUST_STORE_PASSWORD_SYSTEM_PROPERTY).toCharArray();
                String trustStoreLocation = System.getProperty(OPAConstants.TRUST_STORE_LOCATION_SYSTEM_PROPERTY);
                File trustStoreFile = new File(trustStoreLocation);
                try (InputStream localTrustStoreStream = new FileInputStream(trustStoreFile)) {
                    KeyStore trustStore = KeyStore.getInstance("JKS");
                    trustStore.load(localTrustStoreStream, trustStorePassword);
                    SSLContext sslContext = SSLContexts.custom().loadTrustMaterial(trustStore).build();

                    X509HostnameVerifier hostnameVerifier;
                    String hostnameVerifierOption = System.getProperty(OPAConstants.HOST_NAME_VERIFIER);

                    if (OPAConstants.ALLOW_ALL.equalsIgnoreCase(hostnameVerifierOption)) {
                        hostnameVerifier = SSLConnectionSocketFactory.ALLOW_ALL_HOSTNAME_VERIFIER;
                    } else if (OPAConstants.STRICT.equalsIgnoreCase(hostnameVerifierOption)) {
                        hostnameVerifier = SSLConnectionSocketFactory.STRICT_HOSTNAME_VERIFIER;
                    } else {
                        hostnameVerifier = SSLConnectionSocketFactory.BROWSER_COMPATIBLE_HOSTNAME_VERIFIER;
                    }

                    SSLConnectionSocketFactory sslsf = new SSLConnectionSocketFactory(sslContext, hostnameVerifier);
                    Registry<ConnectionSocketFactory> socketFactoryRegistry =
                            RegistryBuilder.<ConnectionSocketFactory>create()
                                    .register(OPAConstants.HTTPS, sslsf).build();
                    poolManager = new PoolingHttpClientConnectionManager(socketFactoryRegistry);
                } catch (IOException | KeyStoreException | CertificateException | NoSuchAlgorithmException | KeyManagementException e) {
                    log.error("Error while reading and setting truststore", e);
                    throw new OPASecurityException(OPASecurityException.INTERNAL_ERROR,
                            "Error while reading and setting truststore", e);
                }
            } else {
                poolManager = new PoolingHttpClientConnectionManager();
            }
            return poolManager;
        }

        /**
         * Return a CloseableHttpClient instance
         *
         * @param url Service endpoint.It can be http/https
         * @return CloseableHttpClient
         * @throws OPASecurityException
         **/
        public CloseableHttpClient createHttpClient(String url) throws OPASecurityException {

            PoolingHttpClientConnectionManager pool;
            try {
                String protocol = new URL(url).getProtocol();
                pool = getPoolingHttpClientConnectionManager(protocol);
            } catch (OPASecurityException | MalformedURLException e) {
                log.error("Error while creating the http client", e);
                throw new OPASecurityException(OPASecurityException.INTERNAL_ERROR,
                        OPASecurityException.INTERNAL_ERROR_MESSAGE, e);
            }

            pool.setMaxTotal(maxOpenConnections);
            pool.setDefaultMaxPerRoute(maxPerRoute);

            //Socket timeout is set to 10 seconds addition to connection timeout.
            RequestConfig params = RequestConfig.custom()
                    .setConnectTimeout(connectionTimeout * 1000)
                    .setSocketTimeout((connectionTimeout + 10) * 10000).build();

            return HttpClients.custom().setConnectionManager(pool).setDefaultRequestConfig(params).build();
        }
    }