Test-Sstpserver

function Test-SstpServer {
<#
    .SYNOPSIS

        Tests whether a server is an SSTP server or not.
    
    .DESCRIPTION
        Tests whether a server is an SSTP server or not.
    
    .PARAMETER Uri
        The Uri of the server - the base i.e. https://vpn.domain.com may be used and the SSTP endpoint will be automatically added.

    .PARAMETER SkipCertificateCheck
        Ignore TLS Certificate errors.
    
    .PARAMETER SstpEndpoint
        The the SSTP specific URI endpoint.

    .OUTPUTS
        System.Boolean
    
    .NOTES
        See https://learn.microsoft.com/en-us/openspecs/windows_protocols/ms-sstp/a4ea5dd9-21e8-41ae-adb9-15bd0a9b991c
#>
    [CmdletBinding()]

    param(
        [Parameter(
            Mandatory=$true
        )]
            [string]$Uri,
        [Parameter()]
            [switch]$SkipCertificateCheck,
        [Parameter(
            DontShow
        )]
            [string]$SstpEndpoint = '/sra_{BA195980-CD49-458b-9E23-C84EE0ADCD75}/'
    )

    process {
        if ($Uri -notmatch $SstpEndpoint) {
            $Uri = $Uri + $SstpEndpoint
        }
        
        $method = New-Object -TypeName System.Net.Http.HttpMethod -ArgumentList 'SSTP_DUPLEX_POST'
        $request_message = New-Object -TypeName System.Net.Http.HttpRequestMessage -ArgumentList $method, $Uri
        $request_message.Version = 1.1

        $handler = New-Object -TypeName System.Net.Http.HttpClientHandler
        
        if ($SkipCertificateCheck){
            $handler.ServerCertificateCustomValidationCallback = [System.Net.Http.HttpClientHandler]::DangerousAcceptAnyServerCertificateValidator
        }

        $client = New-Object -TypeName System.Net.Http.HttpClient -ArgumentList $handler

        Write-Verbose -Message "Testing $Uri"
        try {
            $response = $client.Send($request_message, [System.Net.Http.HttpCompletionOption]::ResponseHeadersRead)
        } catch {
            Write-Error -ErrorAction Stop -Message "TLS Validation error for $Uri"
        }

        $response.StatusCode -eq [System.Net.HttpStatusCode]::OK
    }

}