Intended to help diagnose the following error from Exchange Mitigation Service: "This XML is not deemed safe to consume since Response xml''s signing cert is invalid or not from microsoft""

GetSignedXmlResponseCerts.ps1

$url = "https://officeclient.microsoft.com/getexchangemitigations"

$r = Invoke-WebRequest $url
$x = [xml]$r.Content
$signedXml = New-Object System.Security.Cryptography.Xml.SignedXml($x)
$sigNode = $x.GetElementsByTagName("Signature")
$signedXml.LoadXml([System.Xml.XmlElement] ($sigNode[0]))
$signedXml.Signature.KeyInfo.Certificates | Format-List

$signedXml.Signature.KeyInfo.Certificates | ForEach-Object {
    "Validating certificate: $($_.Subject)"
    $chain = New-Object System.Security.Cryptography.X509Certificates.X509Chain
    if ($chain.Build($_)) {
        "  Validated successfully."
    } else {
        "  Validation failed. ChainStatus:"
        $chain.ChainStatus | Format-Table
    }
}

To run this from Exchange Management Shell, run $exscripts\Get-Mitigations.ps1 first to load the necessary DLLs.