Fix ReadOnlyAttributeUnchangedValidator to handle omitted read-only attributes

When a read-only attribute exists on a user but is not provided in an
update request (value == null), the isUnchanged() method incorrectly
returned false, causing a 400 error with
'updateReadOnlyAttributesRejectedMessage'.

This adds a symmetric null check: if an attribute exists on the user but
was omitted from the request, treat it as unchanged. The existing logic
only handled the reverse case (existingValue == null && isBlank(value)).

Closes keycloak/keycloak#49272

Signed-off-by: Bruce Arctor <5032356+brucearctor@users.noreply.github.com>

services/src/main/java/org/keycloak/userprofile/validator/ReadOnlyAttributeUnchangedValidator.java

@@ -90,12 +90,18 @@ public class ReadOnlyAttributeUnchangedValidator implements SimpleValidator {
         return context;
     }
 
-    private boolean isUnchanged(String existingValue, String value) {
+    // package-private for testing
+    boolean isUnchanged(String existingValue, String value) {
         if (existingValue == null && isBlank(value)) {
             // if attribute not set to the user and value is blank/null, then pass validation
             return true;
         }
 
+        if (existingValue != null && value == null) {
+            // if attribute exists on the user but was not provided in the request, treat as unchanged
+            return true;
+        }
+
         return ObjectUtil.isEqualOrBothNull(existingValue, value);
     }
 

services/src/test/java/org/keycloak/userprofile/validator/ReadOnlyAttributeUnchangedValidatorTest.java

@@ -0,0 +1,70 @@
+/*
+ * Copyright 2024 Red Hat, Inc. and/or its affiliates
+ * and other contributors as indicated by the @author tags.
+ *
+ * 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.keycloak.userprofile.validator;
+
+import org.junit.Assert;
+import org.junit.Test;
+
+/**
+ * Tests for {@link ReadOnlyAttributeUnchangedValidator#isUnchanged(String, String)}.
+ */
+public class ReadOnlyAttributeUnchangedValidatorTest {
+
+    private final ReadOnlyAttributeUnchangedValidator validator = new ReadOnlyAttributeUnchangedValidator();
+
+    @Test
+    public void bothNull() {
+        Assert.assertTrue("both null should be unchanged", validator.isUnchanged(null, null));
+    }
+
+    @Test
+    public void existingNullValueBlank() {
+        Assert.assertTrue("existing null and blank value should be unchanged", validator.isUnchanged(null, ""));
+    }
+
+    @Test
+    public void existingNullValueWhitespace() {
+        Assert.assertTrue("existing null and whitespace value should be unchanged", validator.isUnchanged(null, "   "));
+    }
+
+    @Test
+    public void existingNullValueNonBlank() {
+        Assert.assertFalse("existing null and non-blank value should be changed", validator.isUnchanged(null, "newValue"));
+    }
+
+    @Test
+    public void existingValueAndValueNull_omittedAttribute() {
+        // This is the bug fix: attribute exists on user but was omitted from the update request
+        Assert.assertTrue("existing value with null (omitted) value should be unchanged",
+                validator.isUnchanged("existingValue", null));
+    }
+
+    @Test
+    public void bothEqual() {
+        Assert.assertTrue("equal values should be unchanged", validator.isUnchanged("same", "same"));
+    }
+
+    @Test
+    public void bothDifferent() {
+        Assert.assertFalse("different values should be changed", validator.isUnchanged("old", "new"));
+    }
+
+    @Test
+    public void existingValueAndValueBlank() {
+        Assert.assertFalse("existing value with blank value should be changed", validator.isUnchanged("existingValue", ""));
+    }
+}