Solr should avoid setting system properties that affect the entire JVM. Specifically "javax.security.auth.useSubjectCredsOnly" is one that can cause a bunch of issues if SolrJ is colocated with other Kerberos secured services.
Krb5HttpClientBuilder changes the JVM default to false if it is not set. It is defaulting to true. This affects everything in the JVM. Since SolrJ is meant to be client side, we should avoid doing this.