docs: protected Pair<SamlRegisteredService, SamlRegisteredServiceServiceProviderMetadataFacade> verifySamlAuthenticationRequest(
          final Pair<? extends SignableSAMLObject, MessageContext> authenticationContext,
          final HttpServletRequest request) throws Exception {
          val authnRequest = (AuthnRequest) authenticationContext.getKey();
          val issuer = SamlIdPUtils.getIssuerFromSamlObject(authnRequest);
          LOGGER.debug("Located issuer [{}] from authentication request", issuer);
  
          val registeredService = verifySamlRegisteredService(issuer);
          LOGGER.debug("Fetching saml metadata adaptor for [{}]", issuer);
          val adaptor = SamlRegisteredServiceServiceProviderMetadataFacade.get(
              samlProfileHandlerConfigurationContext.getSamlRegisteredServiceCachingMetadataResolver(), registeredService, authnRequest);
  
          if (adaptor.isEmpty()) {
              LOGGER.warn("No metadata could be found for [{}]", issuer);
              throw new UnauthorizedServiceException(UnauthorizedServiceException.CODE_UNAUTHZ_SERVICE, "Cannot find metadata linked to " + issuer);
          }
  
          val facade = adaptor.get();
          verifyAuthenticationContextSignature(authenticationContext, request, authnRequest, facade);
          SamlUtils.logSamlObject(samlProfileHandlerConfigurationContext.getOpenSamlConfigBean(), authnRequest);
          return Pair.of(registeredService, facade);
      }