Active Directory Federation Services require that the subject name
matches KeyName element when present. While KeyName is beneficial for
Keycloak adapters, it breaks functionality for AD FS as the name
included there is a key ID, not certificate subject expected by AD FS.
This patch contains functionality that excludes KeyName from SAML
messages to identity providers. This behaviour should be made
configurable per client/identity provider and is prepared to do so,
however actual GUI changes are left for a separate patch.
Contrary to POST binding, signature of SAML protocol message sent using
REDIRECT binding is contained in query parameters and not in the
message. This renders <dsig:KeyName> key ID hint unusable. This commit
adds <Extensions> element in SAML protocol message containing key ID so
that key ID is present in the SAML protocol message.
Changes of SAML assertion creation/parsing that are required to allow
for validation of rotating realm key: signed SAML assertions and signed
SAML protocol message now contain signing key ID in XML <dsig:KeyName>
element.
