Migrating custom provider to Quarkus - Implementation of Jakarta REST - ClientBuilder

[niklassc7]

I'm trying to migrate a custom Keycloak authenticator from pre-Quarkus to Keycloak Quarkus.
The old authenticator used JAVA EE (and its Java API for RESTful Web Services) which I replaced with Jakarta EE (and its Jakarta RESTful Web Services / JAX-RS) by replacing all javax* imports with jakarta* and adapting changed methods.

This has worked mostly fine, but in a method for getting an access token from Keycloak, the authenticator has this line:

Client client = ClientBuilder.newClient();

When executed in Keycloak, this throws a

Uncaught server error: java.lang.RuntimeException: java.lang.ClassNotFoundException: Provider for jakarta.ws.rs.client.ClientBuilder cannot be found

If I'm correct, this happens because Jakarta RESTful Web Services is simply a specification and I need a concrete implementation of the ClientBuilder.

In my research I found that there are several implementations, like Jersey or JBoss RESTeasy (Wich Quarkus calls RestEasy Classic), and Quarkus REST (formerly RESTEasy Reactive).
On the Quarkus website it states that the default implementation for Quarkus used to be RestEasy Classic (JBoss RESTEasy) but since version 2.8 it is Quarkus REST which used to be called RESTEasy Reactive.

Since Keycloak 24.0.4 uses Quarkus 3.8.4, I assume I should use Quarkus REST or RESTEasy Reactive.
In the maven repositories I noticed that all the io.quarkus:quarkus-resteasy-reactive* packages were moved to io.quarkus:quarkus-rest* but the oldest version is 3.9.* in the latter. When I want to use the same version of the Quarkus libraries that Keycloak currently ships with (3.8.4), I assume I need to use RESTEasy Reactive and not Quarkus REST.

Here, I however fail to find the appropriate package (e.g. in the maven repository) that provides the implementation for ClientBuilder.
Is my reasoning correct that I should use RESTEasy Reactive version 3.8.4 because the Quarkus version that Keycloak uses, recommends this or is this not relevant for custom providers? Can someone point me to the package and/or javadoc documentation that implements ClientBuilder in the appropriate Jakarta REST implementation?