CreatePWDFileEncryptionKey.ps1

$AESKey = New-Object Byte[] 32
[Security.Cryptography.RNGCryptoServiceProvider]::Create().GetBytes($AESKey)

# file to output the encrypted key too
Set-Content C:\Temp\AzureAutomationPassKey.key $AESKey
Function Get-EncryptedPassword
{
  param (
    [Parameter(Mandatory=$true,HelpMessage='Please specify the key file path')][ValidateScript({Test-Path $_})][String]$KeyPath,
    [Parameter(Mandatory=$true,HelpMessage='Please specify password in clear text')][ValidateNotNullOrEmpty()][String]$Password
  )
  $secPw = ConvertTo-SecureString -AsPlainText $Password -Force
  $AESKey = Get-content $KeyPath
  $Encryptedpassword = $secPw | ConvertFrom-SecureString -Key $AESKey
  $Encryptedpassword
}

$encryptedpass = Get-EncryptedPassword -KeyPath C:\temp\AzureAutomationPassKey.key -Password "thisisntmypassword!"
# Get the encryption string and copy to the clipboard for use in app config 
$encryptedpass | clip