Multi-cert auth failure

[bajnokk]

If an SP has more than one certificates, its authentication fails for some reason, even though the AA is supposed to authenticate against all possible certificates.

This makes the AA unable to work with SPs under a certificate rollover, for example.

[bajnokk]

The module calls SimpleSAML_Utilities::loadPublicKey, that is not only deprecated, but as its name suggests, it returns only one public key of the peer.

SimpleSAML_Configuration::getPublicKeys should be used instead, and the X.509 certificate data should be properly compared. (getPublicKeys returns only the certificate data, not the fingerprint.)