@Override
    public String resolveIssuer(final Optional<OAuthRegisteredService> registeredService) {
        return casProperties.getAuthn().getOauth().getUma().getCore().getIssuer();
    }
This is {@link UmaRequestingPartyTokenSigningService}.

@author Misagh Moayyed
@since 6.0.0
support/cas-server-support-oauth-uma-core/src/main/java/org/apereo/cas/uma/ticket/rpt/UmaRequestingPartyTokenSigningService.java