diff --git a/src/main/java/org/codelibs/fess/sso/oic/OpenIdConnectAuthenticator.java b/src/main/java/org/codelibs/fess/sso/oic/OpenIdConnectAuthenticator.java
index 63ff86fbb..5fb0924b4 100644
--- a/src/main/java/org/codelibs/fess/sso/oic/OpenIdConnectAuthenticator.java
+++ b/src/main/java/org/codelibs/fess/sso/oic/OpenIdConnectAuthenticator.java
@@ -216,6 +216,11 @@ private Object parseArray(JsonParser jsonParser) throws IOException {
                 list.add(parsePrimitive(jsonParser));
             }
         }
+
+        if (list.stream().allMatch(String.class::isInstance)) {
+            return list.toArray(new String[list.size()]);
+        }
+
         return list;
     }
 
diff --git a/src/test/java/org/codelibs/fess/sso/oic/OpenIdConnectAuthenticatorTest.java b/src/test/java/org/codelibs/fess/sso/oic/OpenIdConnectAuthenticatorTest.java
new file mode 100644
index 000000000..1219c35b0
--- /dev/null
+++ b/src/test/java/org/codelibs/fess/sso/oic/OpenIdConnectAuthenticatorTest.java
@@ -0,0 +1,46 @@
+/*
+ * Copyright 2012-2024 CodeLibs Project and the Others.
+ *
+ * Licensed 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.codelibs.fess.sso.oic;
+
+import static org.junit.Assert.assertArrayEquals;
+
+import java.io.IOException;
+import java.util.HashMap;
+import java.util.Map;
+
+import org.codelibs.fess.unit.UnitFessTestCase;
+
+public class OpenIdConnectAuthenticatorTest extends UnitFessTestCase {
+    public void test_parseJwtClaim() throws IOException {
+        // Setup
+        OpenIdConnectAuthenticator authenticator = new OpenIdConnectAuthenticator();
+        final Map<String, Object> attributes = new HashMap<>();
+        String jwtClaim = "{\"sub\":\"1234567890\",\"name\":\"John Doe\",\"groups\":[\"group1\",\"group2\"]}";
+
+        // Execute
+        authenticator.parseJwtClaim(jwtClaim, attributes);
+
+        // Verify
+        assertEquals("1234567890", attributes.get("sub"));
+        assertEquals("John Doe", attributes.get("name"));
+
+        // Check groups array
+        assertTrue(attributes.get("groups") instanceof String[]);
+        String[] groupArray = (String[]) attributes.get("groups");
+        assertArrayEquals(new String[] { "group1", "group2" }, groupArray);
+
+    }
+}