From http://stackoverflow.com/questions/11696944/powershell-v3-invoke-webrequest-https-error

ExportCertificateWithPrivateKey.ps1

Get-ChildItem Cert:\LocalMachine\Root | Where-Object {$_.Subject -eq 'CN=SubjectName'} | Foreach-Object { [system.IO.file]::WriteAllBytes("C:\SSL\SubjectName.pfx",($_.Export('PFX', 'p@ssw0rd')) ) }

Generate Web SSL Cert with makeCert

Makecert -r -pe -n CN="www.website.com" -b 02/01/2014 -e 12/22/2099 -eku 1.3.6.1.5.5.7.3.1 -sky exchange -sp "Microsoft RSA SChannel Cryptographic Provider" -sy 12 -len 4096 -a sha1 website.cer

TrustSSLCertificates.ps1

add-type @"
    using System.Net;
    using System.Security.Cryptography.X509Certificates;
    public class TrustAllCertsPolicy : ICertificatePolicy {
        public bool CheckValidationResult(
            ServicePoint srvPoint, X509Certificate certificate,
            WebRequest request, int certificateProblem) {
            return true;
        }
    }
"@
[System.Net.ServicePointManager]::CertificatePolicy = New-Object TrustAllCertsPolicy

$result = Invoke-WebRequest -Uri "https://IpAddress/resource"