[fix](auth)Compatible with previously enabled ldap configuration (#34891)

fe/fe-common/src/main/java/org/apache/doris/common/LdapConfig.java

@@ -21,6 +21,14 @@ package org.apache.doris.common;
  * LDAP configuration
  */
 public class LdapConfig extends ConfigBase {
+
+    /**
+     * Flag to enable LDAP authentication.
+     */
+    @Deprecated
+    @ConfigBase.ConfField
+    public static boolean ldap_authentication_enabled = false;
+
     /**
      * LDAP server ip.
      */

fe/fe-core/src/main/java/org/apache/doris/mysql/authenticate/AuthenticateType.java

@@ -18,12 +18,17 @@
 package org.apache.doris.mysql.authenticate;
 
 import org.apache.doris.common.Config;
+import org.apache.doris.common.LdapConfig;
 
 public enum AuthenticateType {
     DEFAULT,
     LDAP;
 
     public static AuthenticateType getAuthTypeConfig() {
+        // Compatible with previously enabled ldap configuration
+        if (LdapConfig.ldap_authentication_enabled) {
+            return LDAP;
+        }
         switch (Config.authentication_type.toLowerCase()) {
             case "default":
                 return DEFAULT;

fe/fe-core/src/test/java/org/apache/doris/mysql/authenticate/AuthenticateTypeTest.java

@@ -0,0 +1,57 @@
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The ASF 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.doris.mysql.authenticate;
+
+import org.apache.doris.common.Config;
+import org.apache.doris.common.LdapConfig;
+
+import org.junit.Assert;
+import org.junit.Test;
+
+public class AuthenticateTypeTest {
+
+    @Test
+    public void testGetAuthTypeConfig() {
+        // test default
+        AuthenticateType authTypeConfig = AuthenticateType.getAuthTypeConfig();
+        Assert.assertEquals(AuthenticateType.DEFAULT, authTypeConfig);
+
+        // test old config
+        LdapConfig.ldap_authentication_enabled = true;
+        authTypeConfig = AuthenticateType.getAuthTypeConfig();
+        Assert.assertEquals(AuthenticateType.LDAP, authTypeConfig);
+
+        // test new config
+        LdapConfig.ldap_authentication_enabled = false;
+        Config.authentication_type = "ldap";
+        authTypeConfig = AuthenticateType.getAuthTypeConfig();
+        Assert.assertEquals(AuthenticateType.LDAP, authTypeConfig);
+
+        // test new&old config
+        LdapConfig.ldap_authentication_enabled = true;
+        Config.authentication_type = "ldap";
+        authTypeConfig = AuthenticateType.getAuthTypeConfig();
+        Assert.assertEquals(AuthenticateType.LDAP, authTypeConfig);
+
+        // test default
+        LdapConfig.ldap_authentication_enabled = false;
+        Config.authentication_type = "default";
+        authTypeConfig = AuthenticateType.getAuthTypeConfig();
+        Assert.assertEquals(AuthenticateType.DEFAULT, authTypeConfig);
+    }
+}