SimpleSAMLphp HTTP-Artifact TLS validator confusion allows cross-IdP authentication bypass

Summary SimpleSAMLphp's HTTP-Artifact receive path can treat an unsigned embedded SAML Response as cryptographically valid for the wrong IdP. In the HTTPArtifact::receive flow, the SOAP ArtifactResponse receives a TLS-based validator from SOAPClient::addSSLValidator. The embedded SAML Response th...