@Override
    public Authenticator validateConfig(Map<String, String> config) {
        Objects.requireNonNull(config.get("flowType"), "must provide OAuth2 flow type 'flowType'.");
        return this;
    }
Authenticator for Keycloak OAuth2.

<ul>
  <li>flowType: OAuth2 flow type</li>
  <li>username: if password flow</li>
  <li>password: if password flow</li>
</ul>

Paste JSON config from your Keycloak realm.

@see OAuth2FlowType
@author Marc Savy {@literal <marc@rhymewithgravy.com>}
gateway/engine/vertx-polling/src/main/java/io/apiman/gateway/engine/vertx/polling/fetchers/auth/KeycloakOAuth2.java