AES.ps1

$KeyFile = "AES.key"
$Key = New-Object Byte[] 16   # You can use 16, 24, or 32 for AES
[Security.Cryptography.RNGCryptoServiceProvider]::Create().GetBytes($Key)
$Key | out-file $KeyFile

Create_SecureString.ps1

$PasswordFile = "Password.txt"
$KeyFile = "AES.key"
$Key = Get-Content $KeyFile
$Password = "my_password" | ConvertTo-SecureString -AsPlainText -Force
$Password | ConvertFrom-SecureString -key $Key | Out-File $PasswordFile

DomainJoin.ps1

$domain = "domain_name"
$password = "my_password_plaintext" | ConvertTo-SecureString -asPlainText -Force
$username = "$domain\my_username" 
$credential = New-Object System.Management.Automation.PSCredential($username,$password)
Add-Computer -DomainName $domain -Credential $credential

$domain = "domain_name"
$password = Get-Content "Password.txt"
$AESKeyFilePath = "AES.key"
$AESKey = Get-Content $AESKeyFilePath
$securepassword = $password | ConvertTo-SecureString -key $AESKey
$username = "$domain\my_username" 
$credential = New-Object System.Management.Automation.PSCredential($username,$securepassword)
Add-Computer -DomainName $domain -Credential $credential