[#6499] improvement(server): Support custom configuration options in the REST API /configs

core/src/main/java/org/apache/gravitino/Configs.java

@@ -310,4 +310,12 @@ private Configs() {}
           .version(ConfigConstants.VERSION_0_7_0)
           .stringConf()
           .createWithDefault(SimpleFormatterV2.class.getName());
+
+  public static final ConfigEntry<List<String>> VISIBLE_CONFIGS =
+      new ConfigBuilder("gravitino.server.visibleConfigs")
+          .doc("List of configs that are visible in the config servlet")
+          .version(ConfigConstants.VERSION_0_9_0)
+          .stringConf()
+          .toSequence()
+          .createWithDefault(Collections.emptyList());
 }

core/src/main/java/org/apache/gravitino/config/ConfigConstants.java

@@ -70,4 +70,7 @@ private ConfigConstants() {}
 
   /** The version number for the 0.8.0 release. */
   public static final String VERSION_0_8_0 = "0.8.0";
+
+  /** The version number for the 0.9.0 release. */
+  public static final String VERSION_0_9_0 = "0.9.0";
 }

docs/gravitino-server-config.md

@@ -37,6 +37,7 @@ The `gravitino.conf` file lists the configuration items in the following table.
 | `gravitino.server.shutdown.timeout`                  | Time in milliseconds to gracefully shut down of the Gravitino webserver.                                                                                                              | `3000`                                                                       | No       | 0.2.0            |
 | `gravitino.server.webserver.customFilters`           | Comma-separated list of filter class names to apply to the API.                                                                                                                       | (none)                                                                       | No       | 0.4.0            |
 | `gravitino.server.rest.extensionPackages`            | Comma-separated list of REST API packages to expand                                                                                                                                   | (none)                                                                       | No       | 0.6.0-incubating |
+| `gravitino.server.visibleConfigs`                    | List of configs that are visible in the config servlet                                                                                                                                | (none)                                                                       | No       | 0.9.0-incubating |
 
 The filter in the customFilters should be a standard javax servlet filter.
 You can also specify filter parameters by setting configuration entries of the form `gravitino.server.webserver.<class name of filter>.param.<param name>=<value>`.

server/src/main/java/org/apache/gravitino/server/web/ConfigServlet.java

@@ -22,6 +22,7 @@
 import com.google.common.collect.Maps;
 import java.io.IOException;
 import java.io.PrintWriter;
+import java.util.List;
 import java.util.Map;
 import javax.servlet.http.HttpServlet;
 import javax.servlet.http.HttpServletRequest;
@@ -58,6 +59,15 @@ public ConfigServlet(ServerConfig serverConfig) {
         configs.put(key.getKey(), serverConfig.get(key));
       }
     }
+
+    List<String> visibleConfigs = serverConfig.get(Configs.VISIBLE_CONFIGS);
+
+    for (String config : visibleConfigs) {
+      String configValue = serverConfig.getRawString(config);
+      if (configValue != null) {
+        configs.put(config, configValue);
+      }
+    }
   }
 
   @Override

server/src/test/java/org/apache/gravitino/server/web/TestConfigServlet.java

@@ -22,8 +22,10 @@
 import static org.mockito.Mockito.verify;
 import static org.mockito.Mockito.when;
 
+import com.google.common.collect.Lists;
 import java.io.PrintWriter;
 import javax.servlet.http.HttpServletResponse;
+import org.apache.gravitino.Configs;
 import org.apache.gravitino.server.ServerConfig;
 import org.junit.jupiter.api.Test;
 
@@ -43,4 +45,23 @@ public void testConfigServlet() throws Exception {
             "{\"gravitino.authorization.enable\":false,\"gravitino.authenticators\":[\"simple\"]}");
     configServlet.destroy();
   }
+
+  @Test
+  public void testConfigServletWithVisibleConfigs() throws Exception {
+    ServerConfig serverConfig = new ServerConfig();
+    serverConfig.set(
+        Configs.VISIBLE_CONFIGS,
+        Lists.newArrayList(Configs.AUDIT_LOG_FORMATTER_CLASS_NAME.getKey()));
+    serverConfig.set(Configs.AUDIT_LOG_FORMATTER_CLASS_NAME, "test");
+    ConfigServlet configServlet = new ConfigServlet(serverConfig);
+    configServlet.init();
+    HttpServletResponse res = mock(HttpServletResponse.class);
+    PrintWriter writer = mock(PrintWriter.class);
+    when(res.getWriter()).thenReturn(writer);
+    configServlet.doGet(null, res);
+    verify(writer)
+        .write(
+            "{\"gravitino.audit.formatter.className\":\"test\",\"gravitino.authorization.enable\":false,\"gravitino.authenticators\":[\"simple\"]}");
+    configServlet.destroy();
+  }
 }