docs: swift quickstart improvements as guided by evals flywheel to improve Agentic experience (#1386)

* docs(ios-swift): add CredentialsManager callout in Step 5

* adding warning for not using raw values and use plist based approach

Author: sanchitmehtagit

main/docs/quickstart/native/ios-swift.mdx

@@ -163,7 +163,11 @@ Your AI assistant will automatically create your Auth0 application, fetch creden
   </Step>
 
   <Step title="Create the Authentication Service" stepNumber={5}>
-    Create `AuthenticationService.swift`:
+    Create `AuthenticationService.swift` to handle login, logout, and token storage.
+
+    <Info>
+      **Use `CredentialsManager` for token storage.** The `CredentialsManager` class securely stores credentials in the Keychain and automatically refreshes expired access tokens. Always use it — do not store tokens in memory, `UserDefaults`, or `localStorage`.
+    </Info>
 
     1. Right-click your project → **New File...** → **Swift File**
     2. Name it `AuthenticationService`
@@ -370,6 +374,10 @@ This is **required** for certain features to work properly:
 <Accordion title="Advanced Integration">
 ### Programmatic Configuration
 
+<Warning>
+Never hardcode `clientId` or `domain` values directly in Swift source files — they will be committed to version control. Read them from environment variables or a build-time configuration file at runtime. For most apps, prefer `Auth0.plist` (the default approach in this quickstart).
+</Warning>
+
 Instead of using `Auth0.plist`, you can pass credentials directly in your code. This is useful when credentials need to be dynamic or environment-specific (e.g., different Auth0 tenants for dev/staging/production).
 
 **Replace `Auth0.webAuth()` calls with `Auth0.webAuth(clientId:domain:)`:**