ADDING A TRUSTED ROOT AUTHORITY

The following command creates a new trusted root authority .

$root = New-Object System.Security.Cryptography.X509Certificates.X509Certificate2("c:\temp\YOUR.cer")
New-SPTrustedRootAuthority -Name "Token Signing Root Authority" -Certificate $root

If you receive an error that states that ‘The root of the certificate chain is not a trusted root authority’, like in the image...then you will need to get the root of the certificate and add it to SharePoint’s list of trusted root certificates