@Override
        public OAuth2ClientOptions setSite(String site) {
            if (super.getSite() != null) {
                allowedIssuers.remove(super.getSite());
            }
            allowedIssuers.add(site);
            return super.setSite(site);
        }
Simplified factory to create an {@link io.vertx.ext.auth.oauth2.OAuth2Auth} for OpenID Connect.
<p>
Important modification by msavy: to allow internal/external distinction without freaking out, we have
{@code config.getAllowedIssuers().contains(issuerEndpoint)} with user-provided acceptable issuers.

@author <a href="mailto:plopes@redhat.com">Paulo Lopes</a>
gateway/platforms/vertx3/vertx3/src/main/java/io/apiman/gateway/platforms/vertx3/api/auth/KeycloakDiscovery.java