Determining when your Azure session has expired

Logging into Azure from PowerShell usually gets down with the Add-AzureAccount cmdlet. This pops up a UI form asking for your user name (maybe the account type) and password. Once this completes, you have a token which is good for 24 hours. If you run another Azure targeted script within that time period you don't need to prompt to login again because the token is still valid but if you do you can at least be assured that your script will always have a good credential no matter how annoying that might be for the user of your script. Prompting every 10 minutes for login can be really tiresome.

On the other hand, not prompting can lead to an error message telling you your session has expired, if you try to execute a cmdlet like Set-AzureSubscription, and you should have logged in before running the script.

There doesn't seem to be an officially documented way of determining when the session has expired but I have found a way to do it with minimal code so I thought I would share it.

Fallback

Using the cmdlet Get-AzureSubscription by itself doesn't do anything but return the current (cached) set of subscriptions you have associated with your identity, importantly, it doesn't give you an error if your session has expired. But calling Set-AzureSubscription afterwards will give you the dreaded red error message.

If we combine Get-AzureSubscription with the ExtendedDetails switch and the ErrorAction Stop, we instantly get an exception if the session is not valid and we are then able to prompt for login as before.

Try { # Check current session to see if we are currently logged into Azure
$Subscription = Get-AzureSubscription -ExtendedDetails -ErrorAction Stop
}
Catch { # Exception probably means we need to login again.
Add-AzureAccount
}