RH-SSO SAML adapter support for using keys without a defined KeyName element in IdP SAML descriptor

Issue

• After authentication on IdP (e.g MS ADFS), the SP application goes into error, with the EAP server logs showing:

  2019-12-09 17:33:26,279 DEBUG [org.keycloak.adapters.saml.rotation.SamlDescriptorPublicKeyLocator] (default task-1) Invalid key id: null
  2019-12-09 17:33:26,279 DEBUG [org.keycloak.saml.common] (default task-1) Verification failed for key null: javax.xml.crypto.dsig.XMLSignatureException: the keyselector did not find a validation key
  2019-12-09 17:33:26,279 TRACE [org.keycloak.saml.common] (default task-1) the keyselector did not find a validation key: javax.xml.crypto.dsig.XMLSignatureException: the keyselector did not find a validation key
      at org.apache.jcp.xml.dsig.internal.dom.DOMXMLSignature$DOMSignatureValue.validate(DOMXMLSignature.java:539)
      at org.apache.jcp.xml.dsig.internal.dom.DOMXMLSignature.validate(DOMXMLSignature.java:252)
      at org.keycloak.saml.processing.core.util.XMLSignatureUtil.validateUsingKeySelector(XMLSignatureUtil.java:519)
      at org.keycloak.saml.processing.core.util.XMLSignatureUtil.validateSingleNode(XMLSignatureUtil.java:483)
      at org.keycloak.saml.processing.core.saml.v2.util.AssertionUtil.isSignatureValid(AssertionUtil.java:292)
      at org.keycloak.adapters.saml.profile.AbstractSamlAuthenticationHandler.handleLoginResponse(AbstractSamlAuthenticationHandler.java:378)
      at org.keycloak.adapters.saml.profile.AbstractSamlAuthenticationHandler.handleSamlResponse(AbstractSamlAuthenticationHandler.java:222)
      at org.keycloak.adapters.saml.profile.webbrowsersso.SamlEndpoint.handle(SamlEndpoint.java:44)
      at org.keycloak.adapters.saml.SamlAuthenticator.authenticate(SamlAuthenticator.java:48)
      at org.keycloak.adapters.saml.undertow.AbstractSamlAuthMech.authenticate(AbstractSamlAuthMech.java:132)
          ...
  ...
  2019-12-09 17:33:26,279 TRACE [org.keycloak.saml.common] (default task-1) Could not validate signature using ds:KeyInfo/ds:KeyName hint.
  2019-12-09 17:33:26,279 TRACE [org.keycloak.saml.common] (default task-1) Trying hard to validate XML signature using all available keys.
  ...
  2019-12-09 17:33:26,373 DEBUG [org.keycloak.adapters.saml.rotation.SamlDescriptorPublicKeyLocator] (default task-1) Certificates retrieved from server, filling public key cache
  2019-12-09 17:33:26,373 TRACE [org.keycloak.adapters.saml.rotation.SamlDescriptorPublicKeyLocator] (default task-1) Ignoring certificate null: [
  [
    ...
  ]
  2019-12-09 17:33:26,373 ERROR [org.keycloak.adapters.saml.profile.webbrowsersso.WebBrowserSsoAuthenticationHandler] (default task-1) Failed to verify saml assertion signature
  

• Support for using keys without a defined KeyName