Gets the certificate information for a given host using `System.Net.Sockets.TcpClient`

GetHostCertificateInfo.ps1

<#
.SYNOPSIS
    Gets the certificate information for a given host using System.Net.Sockets.TcpClient
.DESCRIPTION
    Gets the certificate information for a given host, optionally outputting x509 certificate and extended certificate information.
.PARAMETER HostName
    The host to connect to.
.PARAMETER SniHostName
    When the host uses SNI, this authenticates based on the specified SniHostName.
.PARAMETER Port
    The port to connect to.
.PARAMETER SslProtocol
    The protocol to use [Default,Tls,Tls11,Tls12,Tls13,Ssl2,Ssl3].
.PARAMETER FullExceptionOutput
    When an exception occurs, print out the full exception message rather than an overview.
.PARAMETER OutputCertInfo
    Print the Extended information about the certificate (uses openssl - please ensure it is installed beforehand).
.PARAMETER OutputCert
    Print the X509 certificate string.
.EXAMPLE
    Get-HostCertificateInfo -HostName "example.com" -SniHostName "my.example.com" -Port 443 -OutputCertInfo
.Notes
    NAME: Get-HostCertificateInfo
    AUTHOR: Oliver Cooper
    LASTEDIT: 02 October 2021
#>
#function Get-HostCertificateInfo {

    [CmdletBinding()]
    param (
        [Parameter(Mandatory=$true)]
        [string]
        $HostName,

        [string]
        $SniHostName = "",

        [int]
        $Port = 443,

        [Security.Authentication.SslProtocols]
        $SslProtocol = [Security.Authentication.SslProtocols]::None,
    
        [switch]
        $FullExceptionOutput,
        [switch]
        $OutputCertInfo,
        [switch]
        $OutputCert
    )

    function FriendlyErrorString {
        param(
            [string]$Title,

		    [System.Management.Automation.ErrorRecord]$ThisError
	    )

        $Return = new-object System.Text.StringBuilder(256)

        [void]$Return.AppendLine($Title)
        
        [void]$Return.Append("`t-> Message: ")

        if (-Not $ThisError) {
            [void]$Return.AppendLine("N/A")
            Return $Return.ToString()
        }

        if ($FullExceptionOutput.IsPresent) {
            [void]$Return.AppendLine($ThisError.Exception.ToString().Trim())
        } else {
            [void]$Return.AppendLine($ThisError.Exception.Message.Trim())
            if ($ThisError.Exception.InnerException -and $ThisError.Exception.InnerException.InnerException) {
                [void]$Return.Append("`t`t-> ")
                [void]$Return.AppendLine($ThisError.Exception.InnerException.InnerException.Message.Trim())
            }
        }

        [void]$Return.Append("`t-> Method: ")
        [void]$Return.Append($ThisError.InvocationInfo.Line.Trim())
        [void]$Return.Append(" [L")
        [void]$Return.Append($ThisError.InvocationInfo.ScriptLineNumber)
        [void]$Return.Append(":")
        [void]$Return.Append($ThisError.InvocationInfo.OffsetInLine)
        [void]$Return.AppendLine("]")

        Return $Return.ToString()
    }

    [bool]$IsError = $false
    $ErrorString = new-object System.Text.StringBuilder(2000)

    $Certificate = $null
    $TcpClient = New-Object -TypeName System.Net.Sockets.TcpClient
    try {
        # see: https://docs.microsoft.com/en-us/dotnet/api/system.net.security.sslstream?view=net-5.0#code-try-2
        # Create a TCP/IP client socket
        $TcpClient.Connect($HostName, $Port)
        $TcpStream = $TcpClient.GetStream()

        $Callback = {
        # see: https://docs.microsoft.com/en-us/dotnet/api/system.net.security.remotecertificatevalidationcallback?view=net-5.0
        param($sender, $cert, $chain, [System.Net.Security.SslPolicyErrors]$errors) {
                if ($errors -ne [System.Net.Security.SslPolicyErrors]::None) {
                    [void]$ErrorString.AppendLine($(Convert-String -InputObject $errors))
                }
                return $true
            }
        }

        $SslStream = New-Object -TypeName System.Net.Security.SslStream -ArgumentList @($TcpStream, $true, $Callback)
        try {
            $EmptyCertCollection = New-Object -TypeName System.Security.Cryptography.X509Certificates.X509Certificate2Collection
            $SslStream.AuthenticateAsClient($SniHostName, $EmptyCertCollection, $SslProtocol, $false)
            $Certificate = $SslStream.RemoteCertificate

        } catch {
            $IsError = $true
            write-host $Error[0]
            [void]$ErrorString.AppendLine($(FriendlyErrorString 'SSL authentication error' $Error[0]))
            $Error.Clear()
        }
        finally {
            $SslStream.Dispose()
        }

    } catch {
        $IsError = $true
        [void]$ErrorString.AppendLine($(FriendlyErrorString 'TCP connection error' $Error[0]))
    } finally {
        $TcpClient.Dispose()
    }

    if ($Certificate) {

        if ($Certificate -IsNot [System.Security.Cryptography.X509Certificates.X509Certificate2]) {
            $Certificate = New-Object -TypeName System.Security.Cryptography.X509Certificates.X509Certificate2 -ArgumentList $Certificate
        }

        # Format the certificate for openssl to parse
        $X509Cert = [System.Convert]::ToBase64String(
            $Certificate.Export([System.Security.Cryptography.X509Certificates.X509ContentType]::Cert)
        )
    
        $CertStr = new-object System.Text.StringBuilder(2000)
        [void]$CertStr.AppendLine("-----BEGIN CERTIFICATE-----")
        [void]$CertStr.AppendLine($X509Cert)
        [void]$CertStr.AppendLine("-----END CERTIFICATE-----")
    
        #if ($OutputFingerprint.IsPresent) {
            Write-Output $Certificate
            Write-Output ""
        #}
    
        if ($OutputCert.IsPresent) {
            Write-Output $CertStr.ToString()
            Write-Output ""
        }

        if ($OutputCertInfo.IsPresent) {
            # Pass x509 to openssl for decoding
            Write-Output $CertStr.ToString() | openssl x509 -text -noout
        }

    } elseif ($IsError) {
        Write-Warning -Message $ErrorString.ToString()
    }
    else {
        Write-Information "No certificate information found"
    }

#} # END Get-HostCertificateInfo

#Export-ModuleMember -Function Get-HostCertificateInfo