Add util method to get root domain

components/identity-core/org.wso2.carbon.identity.core/src/main/java/org/wso2/carbon/identity/core/util/IdentityUtil.java

@@ -561,6 +561,29 @@ public static boolean isSubdomain(String domainName, String subdomainName) {
         return subdomainName.endsWith("." + domainName);
     }
 
+    /**
+     * Get the root domain of the given domain.
+     * Note: this assumes that the root domain only consists of two parts (eg: wso2.io). The method will not work for
+     * TLDs with more than two parts (eg: wso2.co.uk).
+     *
+     * @param domain Domain.
+     * @return Root domain.
+     */
+    public static String getRootDomain(String domain) {
+
+        if (StringUtils.isBlank(domain)) {
+            return domain;
+        }
+        String[] domainParts = domain.split("\\.");
+        int length = domainParts.length;
+
+        if (length > 2) {
+            return domainParts[length - 2] + "." + domainParts[length - 1];
+        } else {
+            return domain;
+        }
+    }
+
     private static StringBuilder getServerUrlWithPort(String hostName) {
 
         String mgtTransport = CarbonUtils.getManagementTransport();

components/identity-core/org.wso2.carbon.identity.core/src/test/java/org/wso2/carbon/identity/core/util/IdentityUtilTest.java

@@ -838,6 +838,18 @@ public Object[][] getSubdomainData() {
         };
     }
 
+    @DataProvider(name = "rootDomainDataProvider")
+    public Object[][] getRootDomainData() {
+        return new Object[][] {
+                {"dev.api.wso2.io", "wso2.io"},             // Deeper subdomain
+                {"api.test.com", "test.com"},               // Typical subdomain
+                {"abc.com", "abc.com"},                     // Root domain itself
+                {"localhost", "localhost"},                 // Localhost
+                {null, null},                               // Null case
+                {"", ""}                                    // Empty string
+        };
+    }
+
     @Test(dataProvider = "getClockSkewData")
     public void testGetClockSkewInSeconds(String value, int expected) throws Exception {
         Map<String, Object> mockConfiguration = new HashMap<>();
@@ -859,10 +871,18 @@ public void testIsSupportedByUserStore() throws Exception {
 
     @Test(dataProvider = "getSubdomainData")
     public void testCheckSubdomain(String domainName, String subdomainName, boolean expectedResult) throws Exception {
+
         boolean result = IdentityUtil.isSubdomain(domainName, subdomainName);
         assertEquals(result, expectedResult, "Subdomain check failed for: " + domainName + " and " + subdomainName);
     }
 
+    @Test(dataProvider = "rootDomainDataProvider")
+    public void testGetRootDomain(String domain, String expectedRootDomain) {
+
+        String actualRootDomain = IdentityUtil.getRootDomain(domain);
+        assertEquals(actualRootDomain, expectedRootDomain, "Root domain extraction failed for: " + domain);
+    }
+
     private void setPrivateStaticField(Class<?> clazz, String fieldName, Object newValue)
             throws NoSuchFieldException, IllegalAccessException {