[Feature]: Get-AzSubscription with SubscriptionId parameter should internally only get a single subscription instead of listing all subs then searching

[kwill-MSFT]

Description of the new feature

When calling Get-AzSubscription using the SubscriptionId parameter:
Get-AzSubscription -SubscriptionId "123582cb-b98a-4200-a7a5-edee9045a123"

Internally, this executes (GetAzureRMSubscription.cs):
this._client.TryGetSubscriptionById(TenantId, this.SubscriptionId, out result)

TryGetSubscriptionById then executes (RMProfileClient.cs)
var subscriptionList = ListSubscriptions(tenantId).Where(s => s.GetId() == subscriptionIdGuid);

This has the effect of listing all subscriptions that the caller has access to, then finding the matching SubscriptionId. Given that a SubscriptionId is unique, there is no need to list them all then find the first matching one.

For a scenario where the caller has access to thousands of subscriptions, this consumes a lot of unnecessary time and resources since the code internally has to iterate over several nextLink results and call the /subscriptions API multiple times.

Proposed implementation details (optional)

TryGetSubscriptionById should instead utilize TryGetTenantSubscription, which does a single GET on a specific subscription.

This will significantly reduce the resource load on both the client and on ARM since there will be much less data returned and fewer API calls being made.

[dingmeng-xue]

Thanks for reporting. Target to October. Let me set milestone after internal discussion.

[msJinLei]

Resolved in Az.Accounts 2.10.3