PowerShell: Credential with two username formats

2Creds.ps1

# I needed two credential objects, one with username, the other DOMAIN\username.
# Same account, just different formats for username required. 
# Use Get-Credential unless you have a special case like this one. 
$valid_user = $false
# Infinite loop until proper username is entered. 
while (-Not $valid_user) {
    Write-Host "Enter username in DOMAIN\username format." -ForegroundColor DarkCyan
    Write-Host "Press Ctrl+C to exit script." -ForegroundColor DarkCyan
    $username = Read-Host -Prompt "Username"
    $username = $username.Trim()
    $valid_user = $username.Contains("\")
    if (-Not $valid_user) { Write-Host "ERROR! Enter username in DOMAIN\username format." -ForegroundColor Red }    
}

# Read in the password as a Secure String. 
$secureString = Read-Host -AsSecureString -Prompt "Enter password for $username"

# Domain\Username Credential object.
$DomainCred = new-object -typename System.Management.Automation.PSCredential -argumentlist $username,$secureString

# Trim the DOMAIN\ from username.
$username = $username.Substring($username.IndexOf("\")+1)
# Username Credential object. 
$UsernameCred = new-object -typename System.Management.Automation.PSCredential -argumentlist $username,$secureString