@Override
    public List<Credential> getSigningCredentials() {
        return providers.stream()
            .map(Unchecked.function(WsFederationCertificateProvider::getSigningCredentials))
            .flatMap(List::stream)
            .collect(Collectors.toList());
    }
Add provider.

@param provider the provider
support/cas-server-support-wsfederation/src/main/java/org/apereo/cas/support/wsfederation/authentication/crypto/ChainingWsFederationCertificateProvider.java