See the explanation below.
Explanation
Locking prevents other users in your organization from accidentally deleting or modifying critical resources, such as Azure subscription, resource group, or resource.
Note: In Azure, the term resource refers to an entity managed by Azure. For example, virtual machines, virtual networks, and storage accounts are all referred to as Azure resources.
1. In the Settings blade for virtual network VNET, select Locks.

2. To add a lock, select Add.

3. For Lock type select Delete lock, and click OK
Reference:
https://docs.microsoft.com/en-us/azure/azure-resource-manager/resource-group-lock-resources

When you create an AKS cluster, Azure also creates a service principal to support cluster operability with other
Azure resources. You can use this auto-generated service principal for authentication with an ACR registry. To
do so, you need to create an Azure AD role assignment that grants the cluster's service principal access to the
container registry.
References:
https://docs.microsoft.com/bs-latn-ba/azure/container-registry/container-registry-auth-aks

See the explanation below.
Explanation
Step 1: Register the Application
1. Sign in to your Azure Account through the Azure portal.
2. Select Azure Active Directory.
3. Select App registrations.
4. Select New registration.
5. Name the application App10598168 . Select a supported account type, which determines who can use the application. Under Redirect URI, select Web for the type of application you want to create. Enter the URI:
https://www.contoso.com , where the access token is sent to.

6. Click Register
Step 2: Create a new application secret
If you choose not to use a certificate, you can create a new application secret.
7 Select Certificates & secrets.
8. Select Client secrets -> New client secret.
9. Provide a description of the secret, and a duration. When done, select Add.
After saving the client secret, the value of the client secret is displayed. Copy this value because you aren't able to retrieve the key later. You provide the key value with the application ID to sign in as the application.
Store the key value where your application can retrieve it.
Reference:
https://docs.microsoft.com/en-us/azure/active-directory/develop/howto-create-service-principal-portal

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