Contact person may be absent.
Fix WantAssertionSigned
Support for logout requests/responses
According to https://www.oasis-open.org/committees/download.php/35389/sstc-saml-profiles-errata-2.0-wd-06-diff.pdf, 4.1.6 : "The <md:SPSSODescriptor> element's WantAssertionsSigned attribute MAY be used by a service provider to document a requirement that assertions delivered with this profile be signed", so the should_validate_signature should not take this parameter into account.