@Override
    protected String prepareRedirectUrl(final OAuthRegisteredService registeredService,
                                        final String redirectUrl, final Map<String, String> parameters) throws Exception {
        val discovery = casProperties.getAuthn().getOidc().getDiscovery();
        if (registeredService instanceof final OidcRegisteredService oidcService && discovery.isAuthorizationResponseIssuerParameterSupported()) {
            val issuer = issuerService.determineIssuer(Optional.of(oidcService));
            parameters.put(OidcConstants.ISS, issuer);
            return new URIBuilder(redirectUrl)
                .addParameter(OidcConstants.ISS, issuer)
                .build()
                .toString();
        }
        return super.prepareRedirectUrl(registeredService, redirectUrl, parameters);
    }
This is {@link OidcAuthorizationModelAndViewBuilder}.

@author Misagh Moayyed
@since 6.4.0
support/cas-server-support-oidc-core-api/src/main/java/org/apereo/cas/oidc/web/OidcAuthorizationModelAndViewBuilder.java