KEYCLOAK-5032 Forward request parameters to another IdP

Forwarding of prompt and acr_values, if provided in the authorization request.
If prompt is set in the configuration for the identity provider, the configuration overrules the request parameter.

core/src/main/java/org/keycloak/OAuth2Constants.java

@@ -79,6 +79,7 @@ public interface OAuth2Constants {
     String UI_LOCALES_PARAM = "ui_locales";
 
     String PROMPT = "prompt";
+    String ACR_VALUES = "acr_values";
 
     String MAX_AGE = "max_age";