protected String extractProviderId(final HttpServletRequest request) throws MessageDecodingException {
        val providerId = request.getParameter(SamlIdPConstants.PROVIDER_ID);
        if (StringUtils.isBlank(providerId)) {
            LOGGER.warn("No providerId parameter given in unsolicited SSO authentication request.");
            throw new MessageDecodingException("Missing providerId");
        }
        return providerId;
    }
This is {@link SamlIdPInitiatedProfileHandlerController}.

@author Misagh Moayyed
@since 5.0.0
support/cas-server-support-saml-idp-web/src/main/java/org/apereo/cas/support/saml/web/idp/profile/SamlIdPInitiatedProfileHandlerController.java