在 Apache Flink SQL 中，建议使用 Flink 的安全模块来存储凭据和其他机密信息。Flink 的安全模块提供了一个加密的键值存储，可以用于存储敏感数据，例如用户凭据和数据库凭据等。下面是一个简单的示例，演示了如何将用户名和密码保存在 Flink 安全存储中：

import org.apache.flink.api.java.utils.ParameterTool;
import org.apache.flink.runtime.security.DynamicConfigurationLoader;
import org.apache.flink.runtime.security.KerberosConfLoader;
import org.apache.flink.runtime.security.SecurityConfiguration;
import org.apache.flink.runtime.security.SecurityUtils;
import org.apache.flink.runtime.security.modules.JaasModule;
import org.apache.flink.runtime.security.modules.PlainModule;
import org.apache.flink.security.credentials.*;
import org.apache.flink.util.StringUtils;

import java.io.File;
import java.net.URL;
import java.nio.charset.StandardCharsets;
import java.util.concurrent.TimeUnit;

public class FlinkSecretsDemo {

    public static void main(String[] args) throws Exception {
        // Initialize Flink's security module
        SecurityConfiguration sc = new SecurityConfiguration();
        sc.registerModule(JaasModule.class);
        sc.registerModule(PlainModule.class);
        URL securityDir = new File("/path/to/flink/security").toURI().toURL();
        sc.loadFromDirectory(securityDir);

        // Create credentials provider
        CredentialsProvider credentialsProvider = SecurityUtils
                .getInstalledContext()
                .getCredentialsProvider();

        // Store username and password
        String username = "myuser";
        String password = "mypassword";
        byte[] encodedPassword = StringUtils.hexStringToByte(password);
        SecureString securePassword = new SecureString(encodedPassword);
        credentialsProvider.addCredentials(username, new UsernamePasswordCredentials(username, securePassword));

        // Retrieve credentials
        Credentials credentials = credentialsProvider.getCredentials(username);
        System.out.println("Username: " + ((UsernamePasswordCredentials) credentials).getUsername());
        System.out.println("Password: " + ((UsernamePasswordCredentials) credentials).getPassword().toString(StandardCharsets.UTF_8));
    }

}

此示例演示了如