So this is how I do it for a webapp
Set-AzureRmWebApp -ResourceGroupName $ResourceGroup -Name $WebAppName -HostNames @($Alias, $Url);
Which doesn't work for a slot within a web app, like so:
Set-AzureRmWebApp -ResourceGroupName $ResourceGroup -Name $SlotName -HostNames @($SlotAlias, $SlotUrl);
And fails with:
The Resource 'Microsoft.Web/sites/sitename-staging' under resource group 'resgrpname' was not found.
Then there is this Set-AzureRmWebAppSlot but it doesn't have a -HostNames option.
Any help would be greatly appreciated.

