Improved the error message of Az.KeyVault.Extension (Azure#16815)

Author: BethanyZhou

src/KeyVault/KeyVault/Az.KeyVault.Extension/Az.KeyVault.Extension.psm1

@@ -4,20 +4,30 @@
 function Check-SubscriptionLogIn
 {
     param (
-        [string] $SubscriptionId,
-        [string] $AzKVaultName
+        [object] $SubscriptionId,
+        [object] $AzKVaultName
     )
 
+    if("string" -ne $SubscriptionId.GetType().Name)
+    {
+        throw "The type of SubscriptionId should be string, current is " + $SubscriptionId.GetType().Name + ". Please check registration information by 'Get-SecretVault | fl'"
+    }
+
+    if("string" -ne $AzKVaultName.GetType().Name)
+    {
+        throw "The type of AzKVaultName should be string, current is " + $AzKVaultName.GetType().Name + ". Please check registration information by 'Get-SecretVault | fl'"
+    }
+
     $azContext = Az.Accounts\Get-AzContext
-    if (($azContext -eq $null) -or ($azContext.Subscription.Id -ne $SubscriptionId))
+    if (($null -eq $azContext) -or ($azContext.Subscription.Id -ne $SubscriptionId))
     {
         try
         {
             Set-AzContext -SubscriptionId ${SubscriptionId} -ErrorAction Stop
         }
         catch
         {
-            throw "To use ${AzKVaultName} Azure vault, the current user must be logged into Azure account subscription ${SubscriptionId}. Run 'Connect-AzAccount -SubscriptionId ${SubscriptionId}'."
+            throw $_.ToString() + "To use Azure vault named '${AzKVaultName}', please try 'Connect-AzAccount -SubscriptionId {SubscriptionId}' to log into Azure account subscription '${SubscriptionId}'." 
         }
     }
 }
@@ -33,7 +43,7 @@ function Get-Secret
     Check-SubscriptionLogIn $AdditionalParameters.SubscriptionId $AdditionalParameters.AZKVaultName
 
     $secret = Az.KeyVault\Get-AzKeyVaultSecret -Name $Name -VaultName $AdditionalParameters.AZKVaultName
-    if ($secret -ne $null)
+    if ($null -ne $secret)
     {
         switch ($secret.ContentType) {
             'ByteArray' 

src/KeyVault/KeyVault/ChangeLog.md

@@ -18,6 +18,7 @@
         - Additional information about change #1
 -->
 ## Upcoming Release
+* Improved the error message of Az.KeyVault.Extension [#16798]
 * Added default access policies for Key Vault key as "All but purge"
 * Absorbed KeyOps from parameter when importing key from certificate on managed HSM [#16773]
 * Fixed a bug when updating key operations on managed HSM [#16774]