Allow to specify idpHint in Java based applications

This is a feature request similar to https://issues.redhat.com/browse/KEYCLOAK-8600.

I have a Java based web application (I use Spring Boot and Spring Security). Users should be authenticated using a Keycloak realm. The realm is used by multiple applications and allows different authentication "ways".

For my application, I'd like to use a certain authentication way per default. According to the docs, it is possible to do that by appending the parameter "kc_idp_hint=..." to the authentication request.

But I could not find a way to configure my java application so that it appends this parameter when sending the authentication request to Keycloak.

There is an example in the section for the JavaScript adapter, but there is no example in the section about the Java adaptors. Also, my uneducated inspection of the code has shown that it's not possible to configure this.

It would be cool if this would be possible because then we would not need to define a Keycloak realm per desired authentication method.