Adds documentation for connecting to Zookeeper Server with SASL enabled

docs/content/user-manual/configuration/external-integration/_index.cn.md

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+title = "外部集成"
+weight = 4
+chapter = true
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+
+## 简介
+
+ElasticJob 存在部分已知的外部集成，这些集成与 ElasticJob 的 API 基本无关。

docs/content/user-manual/configuration/external-integration/_index.en.md

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+title = "External Integration"
+weight = 4
+chapter = true
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+
+## Introduction
+
+ElasticJob has some known external integrations that are largely unrelated to ElasticJob's API.

docs/content/user-manual/configuration/external-integration/sasl.cn.md

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+title = "连接至开启 SASL 鉴权的 Zookeeper Server"
+weight = 2
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+
+## 使用方式
+
+ElasticJob 的 `org.apache.shardingsphere.elasticjob.reg.zookeeper.ZookeeperRegistryCenter` 能正常连接至开启 SASL 鉴权的 Zookeeper Server。
+SASL 机制允许在客户端和服务器之间实现安全通信，而 ZooKeeper 支持 Kerberos 或 DIGEST-MD5 作为身份验证方案。
+下文讨论常见情景。
+
+### DIGEST-MD5
+
+假设通过 Docker Engine 部署单个 Zookeeper Server 实例，对应的 `docker-compose.yml` 内容如下，
+
+```yaml
+services:
+  zookeeper-test:
+    image: zookeeper:3.9.2
+    volumes:
+      - ./jaas-server-test.conf:/jaas-test.conf
+    environment:
+      JVMFLAGS: "-Djava.security.auth.login.config=/jaas-test.conf"
+      ZOO_CFG_EXTRA: "org.apache.zookeeper.server.auth.SASLAuthenticationProvider sessionRequireClientSASLAuth=true"
+    ports:
+      - "2181:2181"
+```
+
+假设存在文件为 `./jaas-server-test.conf`，内容如下，
+
+```
+Server {
+    org.apache.zookeeper.server.auth.DigestLoginModule required
+    user_bob="bobsecret";
+};
+```
+
+假设存在独立的 Spring Boot 应用，只需要在 Spring Boot 的启动类配置 SASL 的鉴权信息。逻辑类似如下，
+
+```java
+import javax.security.auth.login.AppConfigurationEntry;
+import javax.security.auth.login.Configuration;
+import java.util.HashMap;
+import java.util.Map;
+
+public class ExampleUtils {
+    public void initSasl() {
+        Configuration configuration = new Configuration() {
+            @Override
+            public AppConfigurationEntry[] getAppConfigurationEntry(final String name) {
+                Map<String, String> options = new HashMap<>();
+                options.put("username", "bob");
+                options.put("password", "bobsecret");
+                AppConfigurationEntry entry = new AppConfigurationEntry(
+                        "org.apache.zookeeper.server.auth.DigestLoginModule",
+                        AppConfigurationEntry.LoginModuleControlFlag.REQUIRED,
+                        options);
+                AppConfigurationEntry[] array = new AppConfigurationEntry[1];
+                array[0] = entry;
+                return array;
+            }
+        };
+        Configuration.setConfiguration(configuration);
+    }
+}
+```
+
+此时可正常初始化 ElasticJob 的 `org.apache.shardingsphere.elasticjob.reg.zookeeper.ZookeeperRegistryCenter`。逻辑类似如下，
+
+```java
+import org.apache.shardingsphere.elasticjob.reg.base.CoordinatorRegistryCenter;
+import org.apache.shardingsphere.elasticjob.reg.zookeeper.ZookeeperConfiguration;
+import org.apache.shardingsphere.elasticjob.reg.zookeeper.ZookeeperRegistryCenter;
+
+public class ExampleUtils {
+    public CoordinatorRegistryCenter initElasticJob() {
+        ZookeeperConfiguration zookeeperConfiguration = new ZookeeperConfiguration("127.0.0.1:2181", "test-namespace");
+        CoordinatorRegistryCenter regCenter = new ZookeeperRegistryCenter(zookeeperConfiguration);
+        regCenter.init();
+        return regCenter;
+    }
+}
+```
+
+对于单个 JVM 进程，同一时间只能存在单个 SASL 鉴权信息，因为 Zookeeper Client 通过 JAAS 机制读取 SASL 鉴权信息。
+若当前 Spring Boot 应用需切换到使用不同 SASL 鉴权信息的 Zookeeper Server，则需要注销已有的 SASL 鉴权信息。逻辑类似如下，
+
+```java
+import javax.security.auth.login.Configuration;
+
+public class ExampleUtils {
+    public void exitSasl() {
+        Configuration.setConfiguration(null);
+    }
+}
+```
+
+### Kerberos
+
+要使 ElasticJob 的 `org.apache.shardingsphere.elasticjob.reg.zookeeper.ZookeeperRegistryCenter` 连接至开启 Kerberos 鉴权的 Zookeeper Server，
+流程类似于 DIGEST-MD5。以 https://cwiki.apache.org/confluence/display/ZOOKEEPER/Client-Server+mutual+authentication 为准。
+
+部分地区可能不被允许使用 MIT Kerberos 的源代码或二进制产物，可参考 MIT Kerberos 的分发站点 https://web.mit.edu/kerberos/dist/index.html 。

docs/content/user-manual/configuration/external-integration/sasl.en.md

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+title = "Connect to Zookeeper Server with SASL authentication enabled"
+weight = 2
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+
+## Usage
+
+ElasticJob's `org.apache.shardingsphere.elasticjob.reg.zookeeper.ZookeeperRegistryCenter` can connect to Zookeeper Server with SASL authentication enabled.
+The SASL mechanism allows secure communication between the client and the server, 
+and ZooKeeper supports Kerberos or DIGEST-MD5 as authentication schemes.
+Common scenarios are discussed below.
+
+### DIGEST-MD5
+
+Assuming that a single Zookeeper Server instance is deployed through Docker Engine, 
+the corresponding `docker-compose.yml` content is as follows,
+
+```yaml
+services:
+  zookeeper-test:
+    image: zookeeper:3.9.2
+    volumes:
+      - ./jaas-server-test.conf:/jaas-test.conf
+    environment:
+      JVMFLAGS: "-Djava.security.auth.login.config=/jaas-test.conf"
+      ZOO_CFG_EXTRA: "org.apache.zookeeper.server.auth.SASLAuthenticationProvider sessionRequireClientSASLAuth=true"
+    ports:
+      - "2181:2181"
+```
+
+Assume that there is a file called `./jaas-server-test.conf` with the following content:
+
+```
+Server {
+    org.apache.zookeeper.server.auth.DigestLoginModule required
+    user_bob="bobsecret";
+};
+```
+
+Assuming there is an independent Spring Boot application, 
+users only need to configure SASL authentication information in the Spring Boot startup class. 
+The logic is similar to the following:
+
+```java
+import javax.security.auth.login.AppConfigurationEntry;
+import javax.security.auth.login.Configuration;
+import java.util.HashMap;
+import java.util.Map;
+
+public class ExampleUtils {
+    public void initSasl() {
+        Configuration configuration = new Configuration() {
+            @Override
+            public AppConfigurationEntry[] getAppConfigurationEntry(final String name) {
+                Map<String, String> options = new HashMap<>();
+                options.put("username", "bob");
+                options.put("password", "bobsecret");
+                AppConfigurationEntry entry = new AppConfigurationEntry(
+                        "org.apache.zookeeper.server.auth.DigestLoginModule",
+                        AppConfigurationEntry.LoginModuleControlFlag.REQUIRED,
+                        options);
+                AppConfigurationEntry[] array = new AppConfigurationEntry[1];
+                array[0] = entry;
+                return array;
+            }
+        };
+        Configuration.setConfiguration(configuration);
+    }
+}
+```
+
+At this time, the `org.apache.shardingsphere.elasticjob.reg.zookeeper.ZookeeperRegistryCenter` of ElasticJob can be initialized normally. 
+The logic is similar to the following:
+
+```java
+import org.apache.shardingsphere.elasticjob.reg.base.CoordinatorRegistryCenter;
+import org.apache.shardingsphere.elasticjob.reg.zookeeper.ZookeeperConfiguration;
+import org.apache.shardingsphere.elasticjob.reg.zookeeper.ZookeeperRegistryCenter;
+
+public class ExampleUtils {
+    public CoordinatorRegistryCenter initElasticJob() {
+        ZookeeperConfiguration zookeeperConfiguration = new ZookeeperConfiguration("127.0.0.1:2181", "test-namespace");
+        CoordinatorRegistryCenter regCenter = new ZookeeperRegistryCenter(zookeeperConfiguration);
+        regCenter.init();
+        return regCenter;
+    }
+}
+```
+
+For a single JVM process, only one SASL authentication information can exist at the same time, 
+because Zookeeper Client reads SASL authentication information through the JAAS mechanism.
+If the current Spring Boot application needs to switch to a Zookeeper Server that uses different SASL authentication information, 
+the existing SASL authentication information needs to be deregistered. 
+The logic is similar to the following,
+
+```java
+import javax.security.auth.login.Configuration;
+
+public class ExampleUtils {
+    public void exitSasl() {
+        Configuration.setConfiguration(null);
+    }
+}
+```
+
+### Kerberos
+
+To connect ElasticJob's `org.apache.shardingsphere.elasticjob.reg.zookeeper.ZookeeperRegistryCenter` to Zookeeper Server with Kerberos authentication enabled,
+the process is similar to DIGEST-MD5. 
+Refer to https://cwiki.apache.org/confluence/display/ZOOKEEPER/Client-Server+mutual+authentication .
+
+Some regions may not allow the use of MIT Kerberos source code or binary products. 
+Please refer to the MIT Kerberos distribution site https://web.mit.edu/kerberos/dist/index.html .