$user = "example@gmail.com"
$pass= "examplepassword"
$secpasswd = ConvertTo-SecureString $user -AsPlainText -Force
$cred = New-Object System.Management.Automation.PSCredential ($pass, $secpasswd)

Invoke-RestMethod  'https://www.googleapis.com/gmail/v1/users/me/messages/0' -Method Delete -Credentials $cred