use DefaultAzureCredential instead of AzureCliCredential (#3860)

dotnet/samples/GettingStarted/Agents/Agent_Step09_DependencyInjection/Program.cs

@@ -21,9 +21,12 @@ HostApplicationBuilder builder = Host.CreateApplicationBuilder(args);
 builder.Services.AddSingleton(new ChatClientAgentOptions() { Name = "Joker", ChatOptions = new() { Instructions = "You are good at telling jokes." } });
 
 // Add a chat client to the service collection.
+// WARNING: DefaultAzureCredential is convenient for development but requires careful consideration in production.
+// In production, consider using a specific credential (e.g., ManagedIdentityCredential) to avoid
+// latency issues, unintended credential probing, and potential security risks from fallback mechanisms.
 builder.Services.AddKeyedChatClient("AzureOpenAI", (sp) => new AzureOpenAIClient(
     new Uri(endpoint),
-    new AzureCliCredential())
+    new DefaultAzureCredential())
         .GetChatClient(deploymentName)
         .AsIChatClient());