Could not establish trust relationship for the SSL/TLS Secure Channel – Invoke-WebRequest

I’ve recently been playing around with VMware’s REST APIs in VCSA 6.5 using PowerShell. I’ve been using a lot of Invoke-WebRequest and Invoke-RestMethod to do my work. Chris Wahl has a great primer on how to get started here.

One issue that I ran into very quickly working again my VCSA was a certificate trust relationship error. I’ve run into this error numerous times in the past.

PS F:\Code> Invoke-WebRequest -Uri https://10.0.0.201/rest/com/vmware/cis/session -Method Post -Headers $head
Invoke-WebRequest : The underlying connection was closed: Could not establish trust relationship for the SSL/TLS secure channel.
At line:1 char:1
+ Invoke-WebRequest -Uri https://10.0.0.201/rest/com/vmware/cis/session ...
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ CategoryInfo : InvalidOperation: (System.Net.HttpWebRequest:HttpWebRequest) [Invoke-WebRequest], WebException
+ FullyQualifiedErrorId : WebCmdletWebResponseException,Microsoft.PowerShell.Commands.InvokeWebRequestCommand

The first time I ran into this error I was stumped for while finding a solution. Ultimately it comes down to using Self-Signed Certificates in vCenter, as most of us do.  In general using Invoke-WebRequest or Invoke-RestMethod against a server using a Self-Signed Certificate will cause this error, it’s not just related to vCenter.

The solution is quite simple.  I found a snippet of code some time back that I keep on hand in this situation.  It basically ignores certificate validate in PowerShell allowing you to make a connection with Invoke-WebRequest.  All you have to do it paste this code into your PowerShell session before you run Invoke-WebRequest against a server with a Self-Signed Certificate.

if (-not ([System.Management.Automation.PSTypeName]'ServerCertificateValidationCallback').Type)
{
$certCallback = @"
    using System;
    using System.Net;
    using System.Net.Security;
    using System.Security.Cryptography.X509Certificates;
    public class ServerCertificateValidationCallback
    {
        public static void Ignore()
        {
            if(ServicePointManager.ServerCertificateValidationCallback ==null)
            {
                ServicePointManager.ServerCertificateValidationCallback += 
                    delegate
                    (
                        Object obj, 
                        X509Certificate certificate, 
                        X509Chain chain, 
                        SslPolicyErrors errors
                    )
                    {
                        return true;
                    };
            }
        }
    }
"@
    Add-Type $certCallback
 }
[ServerCertificateValidationCallback]::Ignore()

Once you run the code you will be able to now successfully make a connection.

I’ve seen some simple one liner solutions for Self-Signed Certificates but none of them seemed to work for me.  Whereas the above snippet of code has always worked.  Obviously bypassing certificate validate is not something you want to run on a global scale in PowerShell but this code works great for your current session only.

If there is a simpler way to bypass certificate validation I’d love to hear it.