This script will download FederationMetadata.xml file on the ADFS server and bypass SSL certificate check.

Normally you would download FederationMetadata.xml via

Invoke-WebRequest "https://localhost/FederationMetadata/2007-06/FederationMetadata.xml" -OutFile "federationMetadata.xml"

But instead of this you receive following error message (if you’re using not properly trustable SSL certificate for ADFS FQDN metadata url):

Invoke-WebRequest : The underlying connection was closed: Could not establish trust relationship for the SSL/TLS secure channel.

The right solution to bypass certificate client check is this (remember to run PowerShell as Administrator):

[System.Net.ServicePointManager]::ServerCertificateValidationCallback = {$true}
$WebClient = New-Object System.Net.WebClient
$WebClient.DownloadString("https://localhost/FederationMetadata/2007-06/FederationMetadata.xml") | Out-File -FilePath "C:\federationMetadata.xml" -Encoding utf8