PS use to setup cross farm trust service application

New-CrossFarmTrust.ps1

# https://docs.microsoft.com/en-us/sharepoint/administration/exchange-trust-certificates-between-farms#managing-trust-certificates-by-using-powershell

# 2016 - export the root certificate from the publishing farm

    $2016Root = (Get-SPCertificateAuthority).RootCertificate

    $2016Root.Export("Cert") | Set-Content "F:\Data\2016Root.cer" -Encoding byte



# 2013 - import the root certificate and create a trusted root authority on the consuming farm

    $2016Root = Get-PfxCertificate "F:\Data\2016Root.cer"

    New-SPTrustedRootAuthority "SharePoint 2016 Root" -Certificate $2016Root






# 2013 - export the STS certificate from the consuming farm

    $2013STS = (Get-SPSecurityTokenServiceConfig).LocalLoginProvider.SigningCertificate

    $2013STS.Export("Cert") | Set-Content "F:\Data\2013STS.cer" -Encoding byte


    $2013Root = (Get-SPCertificateAuthority).RootCertificate

    $2013Root.Export("Cert") | Set-Content "F:\Data\2013Root.cer" -Encoding byte

    


# 2016 - import the root certificate and create a trusted root authority on the publishing farm

    $2013Root = Get-PfxCertificate "F:\Data\2013Root.cer"

    New-SPTrustedRootAuthority "SharePoint 2013 Root" -Certificate $2013Root


    $2013STS = Get-PfxCertificate "F:\Data\2013STS.cer"

    New-SPTrustedServiceTokenIssuer "SharePoint 2013 STS" -Certificate $2013STS