Whizlabs needs to enable the Key Vault access for their web application. They just run the following Azure CLI command. 
az webapp identity assign --resource-group wzlabsRG --name wlwebapp 
And got the following result: 
<pre class="brush:java;">{- Finished ..
"principalId": "adb209fe-d414-4232-b954-5cc304071419",
"tenantId": "804c1304-f9a3-5070-89bb-433093104609",
"type": "SystemAssigned",
"userAssignedIdentities": null
}</pre>
WhizLabs is ready to assign permissions to the vault for their webapp: 
az keyvault set-policy --secret-permissions get list --name wzlKV --object-id &lt;SLOT 1&gt; 
What value should they use for the &lt;SLOT 1&gt; ?

Answer options:

A.tenantId
B.subscriptionId
C.principalId
D.applicationId
E.keyvaultId

Correct Answers: C 
az keyvault set-policy --secret-permissions get list --name wzlKV \ 
 --object-id "adb209fe-d414-4232-b954-5cc304071419" 
We need to provide a principalId value for the SLOT 1. 
In the first statement: 
az webapp identity assign --resource-group wzlabsRG --name wlwebapp 
 we are registering our webapp wlwebapp within Azure Active Directory and getting back a unique "registration number" -principalId.PrincipalId is a service principal within our AAD tenant that we can use for RBAC access to Azure resources.
Our web application service principal, or identity, has a type of "System-assigned". The service principal of this type is tied to the web application and will be gone when we delete our application. 
There is another identity type: "User-assigned". This identity is an independent Azure resource. User-assigned identity of the web app will survive if we delete the application. 
In the second statement, we are granting permissions to our web application`s managed identity for get andlist access to wzlKV vault. 
Option A is incorrect since tenantId is an ID of the Azure AD tenant that PrincipalId belongs to. 
All other Options are incorrect. 
For more information about the implementing of Service Principals and Managed Identity, please visit the below URLs: 

https://docs.microsoft.com/en-us/azure/active-directory/managed-identities-azure-resources/overview
https://docs.microsoft.com/en-us/azure/app-service/overview-managed-identity?tabs=dotnet