Could not create SSL/TLS secure channel, despite setting ServerCertificateValidationCallback

Question

I\'m trying to establish SSL/TLS connection to test server with self-signed certificate. Communication through unsecure channel worked without issues.

Answer 1

I came across this thread because I also had the error Could not create SSL/TLS secure channel. In my case, I was attempting to access a Siebel configuration REST API from PowerShell using Invoke-RestMethod, and none of the suggestions above helped.

Eventually I stumbled across the cause of my problem: the server I was contacting required client certificate authentication.

To make the calls work, I had to provide the client certificate (including the private key) with the -Certificate parameter:

$Pwd = 'certificatepassword'
$Pfx = New-Object -TypeName 'System.Security.Cryptography.X509Certificates.X509Certificate2'
$Pfx.Import('clientcert.p12', $Pwd, 'Exportable,PersistKeySet')
Invoke-RestMethod -Uri 'https://your.rest.host/api/' -Certificate $Pfx -OtherParam ...

Hopefully my experience might help someone else who has my particular flavour of this problem.