fix(integration): fix login race conditions in Selenium integration tests

The Selenium test InterpreterModeActionsIT.testPerUserIsolatedAction
fails intermittently due to multiple race conditions in the login flow:

1. The login modal may auto-open on page load when authentication is
   required. Instead of dismissing and re-opening it (which corrupts
   Bootstrap modal state), detect and reuse the already-open modal.

2. sendKeys may not populate the field if Angular hasn't finished
   initializing the form. Fall back to JavaScript-based value injection
   with Angular input event trigger when sendKeys produces empty value.

3. After login, wait for the user dropdown to appear in the navbar
   (positive signal that login succeeded) instead of relying on modal
   invisibility which races with Angular's digest cycle. Then clean up
   any lingering backdrop.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: jongyoul

zeppelin-integration/src/test/java/org/apache/zeppelin/AbstractZeppelinIT.java

@@ -51,17 +51,68 @@ abstract public class AbstractZeppelinIT {
   protected static final long MAX_PARAGRAPH_TIMEOUT_SEC = 120;
 
   protected void authenticationUser(String userName, String password) {
-    clickableWait(
-        By.xpath("//div[contains(@class, 'navbar-collapse')]//li//button[contains(.,'Login')]"),
-        MAX_BROWSER_TIMEOUT_SEC).click();
+    // Check if login modal is already visible (auto-shown when auth is required)
+    boolean modalAlreadyOpen = false;
+    try {
+      manager.getWebDriver().manage().timeouts().implicitlyWait(Duration.ofSeconds(2));
+      WebElement modal = manager.getWebDriver().findElement(By.id("loginModal"));
+      modalAlreadyOpen = modal.isDisplayed();
+    } catch (NoSuchElementException e) {
+      // modal not in DOM yet
+    } finally {
+      manager.getWebDriver().manage().timeouts()
+          .implicitlyWait(Duration.ofSeconds(MAX_BROWSER_TIMEOUT_SEC));
+    }
+
+    if (!modalAlreadyOpen) {
+      clickableWait(
+          By.xpath("//div[contains(@class, 'navbar-collapse')]//li//button[contains(.,'Login')]"),
+          MAX_BROWSER_TIMEOUT_SEC).click();
+    }
+
+    // Wait for the username field inside the modal to be interactable
+    WebElement userNameField = clickableWait(By.xpath("//*[@id='userName']"), MAX_BROWSER_TIMEOUT_SEC);
+    userNameField.clear();
+    userNameField.sendKeys(userName);
+
+    WebElement passwordField = clickableWait(By.xpath("//*[@id='password']"), MAX_BROWSER_TIMEOUT_SEC);
+    passwordField.clear();
+    passwordField.sendKeys(password);
+
+    // Verify credentials were entered — use JS as a fallback if sendKeys didn't work
+    ZeppelinITUtils.sleep(300, false);
+    String enteredUser = userNameField.getAttribute("value");
+    if (enteredUser == null || enteredUser.isEmpty()) {
+      JavascriptExecutor jse = (JavascriptExecutor) manager.getWebDriver();
+      jse.executeScript(
+          "var el = document.getElementById('userName');"
+          + "el.value = arguments[0];"
+          + "angular.element(el).triggerHandler('input');", userName);
+      jse.executeScript(
+          "var el = document.getElementById('password');"
+          + "el.value = arguments[0];"
+          + "angular.element(el).triggerHandler('input');", password);
+      ZeppelinITUtils.sleep(200, false);
+    }
 
-    visibilityWait(By.xpath("//*[@id='userName']"), MAX_BROWSER_TIMEOUT_SEC).sendKeys(userName);
-    visibilityWait(By.xpath("//*[@id='password']"), MAX_BROWSER_TIMEOUT_SEC).sendKeys(password);
     clickableWait(
         By.xpath("//*[@id='loginModalContent']//button[contains(.,'Login')]"),
         MAX_BROWSER_TIMEOUT_SEC).click();
 
-    ZeppelinITUtils.sleep(1000, false);
+    // Wait for the logged-in navbar user dropdown to appear (confirms login success)
+    visibilityWait(
+        By.xpath("//div[contains(@class, 'navbar-collapse')]//li//button[contains(@class, 'nav-btn dropdown-toggle ng-scope')]"),
+        MAX_BROWSER_TIMEOUT_SEC);
+
+    // Dismiss any lingering modal backdrop via JavaScript
+    try {
+      ((JavascriptExecutor) manager.getWebDriver()).executeScript(
+          "document.querySelectorAll('.modal-backdrop').forEach(e => e.remove());"
+          + "$('#loginModal').modal('hide');");
+    } catch (Exception e) {
+      // ignore if jQuery/Bootstrap not ready
+    }
+    ZeppelinITUtils.sleep(500, false);
   }
 
   protected void logoutUser(String userName) throws URISyntaxException {