Update AKS Arc Terraform doc for az login

Author: HJ Hang

AKS-Arc/create-clusters-terraform.md

@@ -51,7 +51,11 @@ To create an SSH key pair (same as Azure AKS), use the following procedure:
 
 ## Sign in to Azure
 
-Terraform only supports authenticating to Azure with the Azure CLI. Authenticating using Azure PowerShell isn't supported. Therefore, while you can use the Azure PowerShell module when doing your Terraform work, you must first [authenticate to Azure](/azure/developer/terraform/authenticate-to-azure).
+Terraform only supports authenticating to Azure with the Azure CLI using [`az login`](https://learn.microsoft.com/en-us/cli/azure/reference-index?view=azure-cli-latest#az-login). Authenticating using Azure PowerShell isn't supported. Therefore, while you can use the Azure PowerShell module when doing your Terraform work, you must first [authenticate to Azure](/azure/developer/terraform/authenticate-to-azure).
+
+  ```azurecli
+   az login 
+   ```
 
 ## Implement the Terraform code
 
@@ -114,9 +118,9 @@ Run [`terraform init`](https://www.terraform.io/docs/commands/init.html) to
 terraform init -upgrade
 ```
 
-## Create a Terraform execution plan and apply the plan
+## Create a Terraform execution plan and apply
 
-Run [terraform plan](https://www.terraform.io/docs/commands/plan.html) to create an execution plan, then run [terraform apply](https://www.terraform.io/docs/commands/apply.html) to apply the output file to your cloud infrastructure:
+Please make sure you've run [`az login`](https://learn.microsoft.com/en-us/cli/azure/reference-index?view=azure-cli-latest#az-login) and authenticate to Azure before this step, otherwise there will be failure when applying the Terraform plan. Run [terraform plan](https://www.terraform.io/docs/commands/plan.html) to create an execution plan, then run [terraform apply](https://www.terraform.io/docs/commands/apply.html) to apply the output file to your cloud infrastructure:
 
 ```terraform
 terraform plan -out main.tfplan