...
Metadata signature verification is done against the public key alone. If the public key for the federation metadata feed channel is supplied in the form of an X.509 certificate, other aspects of the certificate such as its expiry date do not form part of signature verification. This approach is borrowed from the SAML metadata interoperability profile [SAMLMetaIoP] (url?). In particular an expired certificate will still be used for the verification purpose. (Some text is missing to introduce next table)
Metadata signature verification includes following checks:
...