Azure API Management backup automation

Backup-AzureAPIM.ps1

<#
.SYNOPSIS
	This Azure Automation runbook automates Azure API Management backup to Blob storage and deletes old backups from blob storage. 

.DESCRIPTION
	You should use this Runbook if you want manage Azure API Management backups in Blob storage. 
	This is a PowerShell runbook, as opposed to a PowerShell Workflow runbook. 
	It requires AzureRM.ApiManagement module to be installed.
	The script uses the AzureRunAsConnection connection to login and perform the backup.

.PARAMETER ApimResourceGroupName
	Specifies the name of the resource group where the Azure Api Management instance is located.
	
.PARAMETER ApimInstanceName
	Specifies the name of the Azure Api Management which script will backup.

.PARAMETER StorageAccountName
	Specifies the name of the storage account where backup file will be uploaded.

.PARAMETER StorageAccountKey
	Specifies the key of the storage account where backup file will be uploaded.

.PARAMETER BlobContainerName
	Specifies the container name of the storage account where backup file will be uploaded. Container will be created 
	if it does not exist.

.PARAMETER BackupFilePrefix
	Specifies the backup blob file prefix. The suffix will be automatically generated based on the date in the format 
	yyyyMMddHHmm followed by the .bak file extension. Default value apim_.

.PARAMETER RetentionDays
	Specifies the number of days how long backups are kept in blob storage. The default value is 30 days as the backups 
	expire after that. Script will remove all older files from container, thus a dedicated container should be used 
	for this script.

.INPUTS
	None.

.OUTPUTS
	Human-readable informational and error messages produced during the job. Not intended to be consumed by another runbook.

#>

param(
    [parameter(Mandatory=$true)]
    [String] $ApimResourceGroupName,
    [parameter(Mandatory=$true)]
    [String] $ApimInstanceName,
    [parameter(Mandatory=$true)]
    [String]$StorageAccountName,
    [parameter(Mandatory=$true)]
    [String]$StorageAccountKey,
    [parameter(Mandatory=$true)]
    [string]$BlobContainerName,
    [parameter(Mandatory=$false)]
    [string]$BackupFilePrefix = "apim_",
    [parameter(Mandatory=$false)]
    [Int32]$RetentionDays = 30
)

$ErrorActionPreference = 'stop'

function Login() {
	$connectionName = "AzureRunAsConnection"
	try
	{
		Write-Verbose "Acquiring service principal for connection '$connectionName'" -Verbose

		$servicePrincipalConnection = Get-AutomationConnection -Name $connectionName         

		Write-Verbose "Logging in to Azure..." -Verbose

		Add-AzureRmAccount `
			-ServicePrincipal `
			-TenantId $servicePrincipalConnection.TenantId `
			-ApplicationId $servicePrincipalConnection.ApplicationId `
			-CertificateThumbprint $servicePrincipalConnection.CertificateThumbprint | Out-Null
	}
	catch {
		if (!$servicePrincipalConnection)
		{
			$ErrorMessage = "Connection $connectionName not found."
			throw $ErrorMessage
		} else{
			Write-Error -Message $_.Exception
			throw $_.Exception
		}
	}
}

function Create-Blob-Container([string]$blobContainerName, $storageContext) {
	Write-Verbose "Checking if blob container '$blobContainerName' already exists" -Verbose
	if (Get-AzureStorageContainer -ErrorAction "Stop" -Context $storageContext | Where-Object { $_.Name -eq $blobContainerName }) {
		Write-Verbose "Container '$blobContainerName' already exists" -Verbose
	} else {
		New-AzureStorageContainer -ErrorAction "Stop" -Name $blobContainerName -Permission Off -Context $storageContext
		Write-Verbose "Container '$blobContainerName' created" -Verbose
	}
}

function Backup-To-Blob-Storage([string]$apimResourceGroupName, [string]$apimInstanceName, $storageContext, [string]$blobContainerName, [string]$backupPrefix) {

	$backupBlobName = $backupPrefix + (Get-Date).ToString("yyyyMMddHHmm") + ".bak"

	Write-Verbose "Starting APIM backup to blob '$blobContainerName/$backupBlobName'" -Verbose

	Backup-AzureRmApiManagement -Name $apimInstanceName -ResourceGroupName $apimResourceGroupName -StorageContext $storageContext `
                       -TargetContainerName $blobContainerName `
                       -TargetBlobName $backupBlobName
}

function Delete-Old-Backups([int]$retentionDays, [string]$blobContainerName, $storageContext) {
	Write-Output "Removing backups older than '$retentionDays' days from container: '$blobContainerName'"
	$isOldDate = [DateTime]::UtcNow.AddDays(-$retentionDays)
	$blobs = Get-AzureStorageBlob -Container $blobContainerName -Context $storageContext
	foreach ($blob in ($blobs | Where-Object { $_.LastModified.UtcDateTime -lt $isOldDate -and $_.BlobType -eq "BlockBlob" })) {
		Write-Verbose ("Removing blob: " + $blob.Name) -Verbose
		Remove-AzureStorageBlob -Blob $blob.Name -Container $blobContainerName -Context $storageContext
	}
}

Write-Verbose "Starting APIM backup" -Verbose

Write-Verbose "Establishing storage context" -Verbose
$StorageContext = New-AzureStorageContext -StorageAccountName $storageAccountName -StorageAccountKey $StorageAccountKey

Login

Create-Blob-Container `
	-blobContainerName $blobContainerName `
	-storageContext $storageContext
	
Backup-To-Blob-Storage `
	-apimResourceGroupName $ApimResourceGroupName `
    -apimInstanceName $ApimInstanceName `
    -storageContext $StorageContext `
    -blobContainerName $BlobContainerName `
    -backupPrefix $BackupFilePrefix
	
Delete-Old-Backups `
	-retentionDays $RetentionDays `
	-storageContext $StorageContext `
	-blobContainerName $BlobContainerName
	
Write-Verbose "APIM backup script finished" -Verbose

I keep getting issues when the backup-azurermapimanagement cmdlet is run. I get the following error saying something about an invalid cast. I'm thinking it's when referencing the storagecontext variable in the cmdlet. Help?
The running command stopped because the preference variable "ErrorActionPreference" or common parameter is set to Stop: System.Management.Automation.ParameterBindingException: Cannot bind parameter 'StorageContext'. Cannot convert the "Microsoft.WindowsAzure.Commands.Common.Storage.AzureStorageContext" value of type "Microsoft.WindowsAzure.Commands.Common.Storage.AzureStorageContext" to type "Microsoft.Azure.Commands.Common.Authentication.Abstractions.IStorageContext". ---> System.Management.Automation.PSInvalidCastException: Cannot convert the "Microsoft.WindowsAzure.Commands.Common.Storage.AzureStorageContext" value of type "Microsoft.WindowsAzure.Commands.Common.Storage.AzureStorageContext" to type "Microsoft.Azure.Commands.Common.Authentication.Abstractions.IStorageContext". at System.Management.Automation.LanguagePrimitives.ThrowInvalidCastException(Object valueToConvert, Type resultType) at System.Management.Automation.LanguagePrimitives.ConvertNoConversion(Object valueToConvert, Type resultType, Boolean recurse, PSObject originalValueToConvert, IFormatProvider formatProvider, TypeTable backupTable) at System.Management.Automation.LanguagePrimitives.ConversionData`1.Invoke(Object valueToConvert, Type resultType, Boolean recurse, PSObject originalValueToConvert, IFormatProvider formatProvider, TypeTable backupTable) at System.Management.Automation.LanguagePrimitives.ConvertTo(Object valueToConvert, Type resultType, Boolean recursion, IFormatProvider forma

I found that I needed to supply the subscription name in the Auth function. I have updated the script in my fork here: https://gist.github.com/mikedizzle/1d4f012857b654f301ab7f1047b56ea8