<#
.Synopsis
   Reads RDP Certificate information
.DESCRIPTION
   This script connects to a remote host to read and return the RDP certificate information
.EXAMPLE
   Read-RDPCert -Computer "PC1,PC2".Split(",") -Verbose
   Get the RDP certificate information for PC1 and PC2
.EXAMPLE
   Another example of how to use this cmdlet
.NOTES
Alan Kaplan 6/12/2017
Based on code and comments found at 
https://blogs.technet.microsoft.com/parallel_universe_-_ms_tech_blog/2014/06/26/~
reading-a-certificate-off-a-remote-ssl-server-for-troubleshooting-with-powershell/
#>

Function Read-RDPCert
{
    [CmdletBinding()]
    param(
    [parameter(
    Mandatory=$true,
    ValueFromPipeline=$true
    )]
    [string[]]$Computer,
    [parameter(Mandatory=$False)]
    [int]$Port = 3389
    ) 
 
Begin
{
}

Process
{
  Foreach ($computerName in $Computer){
    Try{
        #Create a TCP Socket to the computer and a port number
        $tcpsocket = New-Object Net.Sockets.TcpClient($computerName, $port) -ErrorAction stop
        #Socket Got connected get the tcp stream ready to read the certificate
        Write-Verbose "Successfully Connected to $computername on $port" 
        $tcpstream = $tcpsocket.GetStream()
        Write-Verbose "Reading SSL Certificate…."
   
        #Create an SSL Connection 
        $sslStream = New-Object System.Net.Security.SslStream($tcpstream,$false, {
        param($sender, $certificate, $chain, $sslPolicyErrors) 
        return $true
        })

        #Force the SSL Connection to send us the certificate
        $sslStream.AuthenticateAsClient($computerName) 

        #Read the certificate
        $certinfo = New-Object system.security.cryptography.x509certificates.x509certificate2($sslStream.RemoteCertificate)

        [PSCustomObject]@{
        ComputerName = $computername
        #DnsNameList = $certinfo.DnsNameList -join ";"
        #Issuer = $certinfo.Issuer
        Subject = $certinfo.Subject
        NotBefore = $certinfo.NotBefore
        NotAfter =$certinfo.NotAfter
        SerialNumber = $certinfo.SerialNumber
        Thumbprint = $certinfo.Thumbprint
        Result = 'Success'
        }
    }
    Catch
    {
        #If any failures, parse and return error message
        $err = $Error[0].Exception.Message.Split(':')[1].Replace('"','').Trim()
        Write-Verbose $err
        [PSCustomObject]@{
            ComputerName = $computername
            #DnsNameList = ''
            #Issuer = ''
            Subject = ''
            NotBefore = ''
            NotAfter =''
            SerialNumber = ''
            Thumbprint = ''
            Result = $Err
        }
      }
    }#end For
   }#end Process
   End 
   {
   }
}