$xml = XML::LibXML->load_from_file(..);
my $signer = XML::Sig->new({
x509=>1
   });
If($signer->verify($xml)) {
}
Eg Assertion XML from WIF:
  <Assertion ID="abc">
    <bar>123</bar>
    <Signature xmlns="http://www.w3.org/2000/09/xmldsig#">
      <SignedInfo xmlns="http://www.w3.org/2000/09/xmldsig#" xmlns:samlp="urn:oasis:names:tc:SAML:2.0:protocol" xmlns:xenc="http://www.w3.org/2001/04/xmlenc#">
        <CanonicalizationMethod Algorithm="http://www.w3.org/TR/2001/REC-xml-c14n-20010315#WithComments" />
        <SignatureMethod Algorithm="http://www.w3.org/2000/09/xmldsig#rsa-sha1" />
        <Reference URI="#abc">
          <Transforms>
            <Transform Algorithm="http://www.w3.org/2000/09/xmldsig#enveloped-signature" />
          </Transforms>
          <DigestMethod Algorithm="http://www.w3.org/2000/09/xmldsig#sha1" />
          <DigestValue>9kpmrvv3peVJpNSTRycrV+jeHVY=</DigestValue>
        </Reference>
      </SignedInfo>
      <SignatureValue>
        HXUBnMgPJf//j4ihaWnaylNwAR5AzDFY83HljFIlLmTqX1w1C72ZTuRObvYve8TNEbVsQlTQkj4R
        hiY0pgIMQUb75GLYFtc+f0Y.......xwCdyGsIZOIZdQ8MWpeQrifxBR0d8W1Zm6ix21WNv
        ONt575h7VxLKw8BDhNPS0p8CS3hOnSk29stpiDMCHFPxAwrbKVL1kGDLaLZn1q8nNRmH8oFxG15l
        UmS3JXDZAss8gZhU7g9T4XllCqjrAvzPLOFdeQ==
      </SignatureValue>
      <KeyInfo>
        <X509Data><X509Certificate>
MIICajCCAdOgAwIBAgIBADANBg.....00m0YZGyc4LzgD0CROMASTWNg==</X509Certificate></X509Data>
</KeyInfo>
  
    </Signature>
  </Assertion>