A PowerShell script for retrieving public certificates from remote websites.

Get-PublicKey.ps1

function Get-PublicKey
{
# https://stackoverflow.com/questions/22233702/how-to-download-the-ssl-certificate-from-a-website-using-powershell

    [OutputType([System.Security.Cryptography.X509Certificates.X509Certificate])]
    PARAM (
        [Uri]$Uri
    )

    if (-Not ($uri.Scheme -eq "https"))
    {
        Write-Error "You can only get keys for https addresses"
        return
    }

    $request = [System.Net.HttpWebRequest]::Create($uri)

    try
    {
        #Make the request but ignore (dispose it) the response, since we only care about the service point
        $request.GetResponse().Dispose()
    }
    catch [System.Net.WebException]
    {
        if ($_.Exception.Status -eq [System.Net.WebExceptionStatus]::TrustFailure)
        {
            #We ignore trust failures, since we only want the certificate, and the service point is still populated at this point
        }
        else
        {
            #Let other exceptions bubble up, or write-error the exception and return from this method
            throw
        }
    }

    #The ServicePoint object should now contain the Certificate for the site.
    $servicePoint = $request.ServicePoint
    $certificate = $servicePoint.Certificate
    
    Return $certificate
}