Add docs for specifying Selenium Grid URL securely

content/docs/2.9/scalers/selenium-grid-scaler.md

@@ -18,7 +18,7 @@ The below is an example trigger configuration for chrome node.
 triggers:
   - type: selenium-grid
     metadata:
-      url: 'http://selenium-hub:4444/graphql' # Required
+      url: 'http://selenium-hub:4444/graphql' # Required. Can be ommitted if specified via TriggerAuthentication/ClusterTriggerAuthentication.
       browserName: 'chrome'  # Required
       browserVersion: '91.0' # Optional. Only required when supporting multiple versions of browser in your Selenium Grid.
       unsafeSsl : 'true' # Optional
@@ -143,3 +143,49 @@ spec:
         browserName: 'chrome'
         browserVersion: '90.0'
 ```
+
+### Authentication Parameters
+
+It is possible to specify the Graphql url of your Selenium Grid using authentication parameters. This useful if you have enabled Selenium Grid's Basic HTTP Authentication and would like to keep your credentials secure.
+
+- `url` - Graphql url of your Selenium Grid. Refer to the Selenium Grid's documentation [here](https://www.selenium.dev/documentation/en/grid/grid_4/graphql_support/) for more info.
+
+```yaml
+apiVersion: v1
+kind: Secret
+metadata:
+  name: selenium-grid-secret
+  namespace: keda
+type: Opaque
+data:
+  graphql-url: base64 encoded value of GraphQL URL
+---
+apiVersion: keda.sh/v1alpha1
+kind: TriggerAuthentication
+metadata:
+  name: keda-trigger-auth-selenium-grid-secret
+  namespace: keda
+spec:
+  secretTargetRef:
+  - parameter: url
+    name: selenium-grid-secret
+    key: graphql-url
+---
+apiVersion: keda.sh/v1alpha1
+kind: ScaledObject
+metadata:
+  name: selenium-grid-chrome-scaledobject
+  namespace: keda
+  labels:
+    deploymentName: selenium-chrome-node
+spec:
+  maxReplicaCount: 8
+  scaleTargetRef:
+    name: selenium-chrome-node
+  triggers:
+    - type: selenium-grid
+      metadata:
+        browserName: 'chrome'
+      authenticationRef:
+        name: keda-trigger-auth-selenium-grid-secret
+```