Solr is getting support for more authentication plugins year by year, and customers have developed their own in-house plugins as well.
At the same time we see more and more JIRAs to add BasicAuth support for various clients and use cases, such as
SOLR-12584 (Solr Exporter), SOLR-9779 (Streaming expressions), SOLR-11356 (ConcurrentUpdateSolrClient), SOLR-8213 (JDBC), SOLR-12583 (Subquery docTransformer) and SOLR-10322 (Streaming expression daemon), SOLR-12860 (metrics history), SOLR-11759 (DocExpirationUpdateProcessor), SOLR-11959 (CDCR), SOLR-12359 (LIR) and probably more. Some of these may be bugs that can be fixed with PKI though...
Currently the framework supports only one active Auth method (except PKI which is special). Which means that if you use something else than BasicAuth, you're lucky if you get any of the above features to work with your cluster.
Even the AdminUI only supports BasicAuth (implicit via browser). Admin UI has explicit support for a few plugins only.
I think the solution is to allow more than one auth plugin to be active at the same time, allowing people to use their custom fancy auth which is tightly integrated with their environment, and at the same time activate e.g. BasicAuth or JWTAuth for use with other clients that do not support the primary auth method.