$certParams =
@{
  Type              = 'Custom'
  KeyUsage          = 'DigitalSignature'
  FriendlyName      = 'WindowsTerminal'
  CertStoreLocation = 'Cert:\LocalMachine\My'
  Subject           = (
                        'CN=Microsoft Corporation',
                        'O=Microsoft Corporation',
                        'L=Redmond',
                        'S=Washington',
                        ' C=US'
                      ) -join ','
  TextExtension     = (
                        '2.5.29.37={text}1.3.6.1.5.5.7.3.3',
                        '2.5.29.19={text}'
                      )
}

$password = 'changeme'

$certExportParams =
@{
  FilePath = 'WindowsTerminal.pfx'
  Password = ConvertTo-SecureString -String $password -Force -AsPlainText
  Cert     = "Cert:\LocalMachine\My\$(
                                       New-SelfSignedCertificate @certParams `
                                       | Select-Object -ExpandProperty Thumbprint
                                     )"
}
Export-PfxCertificate @certExportParams

Remove-Item -Path $certExportParams.Cert

$signTool    = Get-Item 'C:\Program Files (x86)\Windows Kits\10\bin\*\x86\SignTool.exe'
$packageName = Get-Item CascadiaPackage_*_x64.msix `
               | Select-Object -ExpandProperty Name

& $signTool sign /fd SHA256 `
                 /a `
                 /f $certExportParams.FilePath `
                 /p $password `
                 $packageName