powershell code signing: Set-AuthenticodeSignature : Cannot bind parameter 'Certificate'. Cannot convert value - powershell

Question

Trying to create a self-signed code signing certificate that I can use to sign powershell scripts... Looks like it works except when I try to use the certificate to sign a powershell scriptit gives me the Error "Set-AuthenticodeSignature : Cannot bind parameter 'Certificate'. Cannot convert value "
Here's the code that reproduces the problem:
# FILE: new_code_signing_cert.ps1
param(
[switch]$trace
)
try {
if ($trace) {
Set-PSDebug -Trace 1
}
$base = "wpmoore_code_signing";
$password = "password123";
$outdir = ".\cert"
$splat = #{
Subject = "CN=Script Automation,E=myemail#gmail.com,O=My Name"
FriendlyName = "$base"
NotAfter = (Get-Date).AddYears(3)
CertStoreLocation = "Cert:\CurrentUser\My"
Type = "CodeSigningCert"
}
write-host "Creating Code Signing Certificate...`n"
$cert = New-SelfSignedCertificate #splat
$cthumb = $cert.Thumbprint
$cpath = "Cert:\CurrentUser\My\$cthumb"
# Backup Certificate with password
$encrypted = ConvertTo-SecureString -String $password -Force -AsPlainText
new-Item -Path $outdir -Type Directory -ErrorAction SilentlyContinue | out-null
$pfx_file = "${outdir}\${base}.${cthumb}.pfx"
Export-PfxCertificate -Cert:$cpath -FilePath:$pfx_file -Password $encrypted | out-null
write-host "Certificate Location : $cpath"
write-host "Certificate Backup : $pfx_file"
# Dir of CertStoreLocation
#Get-ChildItem $cpath
Set-AuthenticodeSignature -Certificate $cpath -FilePath .\new_code_signing_cert.ps1
}
finally {
Set-PSDebug -Trace 0
write-host ""
}
Hwere's what happens when I run...
PS> new_code_signing_cert.ps1
Set-AuthenticodeSignature : Cannot bind parameter 'Certificate'. Cannot convert value
"Cert:\CurrentUser\My\C4C3179BAB17C20F33D3D0E23CF88CF500CDBD68" to type
"System.Security.Cryptography.X509Certificates.X509Certificate2". Error: "The given path's format is not
supported."
At line:1 char:40
+ ... Certificate Cert:\CurrentUser\My\C4C3179BAB17C20F33D3D0E23CF88CF500CD ...
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ CategoryInfo : InvalidArgument: (:) [Set-AuthenticodeSignature], ParameterBindingException
+ FullyQualifiedErrorId : CannotConvertArgumentNoMessage,Microsoft.PowerShell.Commands.SetAuthenticodeSig
natureCommand

Answer 1

Re-Loading certificate using Cert path:
$cert2 = Get-ChildItem -Path $cpath -CodeSigningCert
Re-Loading certificate from pfx file:
$cert2 = Get-PfxCertificate -FilePath $pfx_file
Once you have the certificate loaded:
Set-AuthenticodeSignature -Certificate $cert2 -FilePath script.ps1
Or use the certificate already loaded:
Set-AuthenticodeSignature -Certificate $cert -FilePath script.ps1