We use Solr 6.6.3. Recently on one network when switching on authentication (security.json) began experiencing significant delays (5-10 seconds) to fulfill each request to /solr index.
I debugged the issue and it was essentially triggered by line 456 of SolrDispatchFilter.java:
The issue is that on machines and networks with poor configuration or DNS issues in particular, request.getLocalName() can trigger expensive reverse DNS queries for the ethernet interfaces, and will only return within reasonable timeframe if manually written into /etc/hosts.
More to the point, request.getLocalName() should be considered an expensive operation in general, and in SolrDispatchFilter it runs unconditionally even if debug is disabled.
I would suggest to either replace request.getLocalName/Port here, or at the least, wrap the debug operation so it doesn't affect any production systems:
The authenticateRequest method in question is private so we could not override it and making another HttpServletRequestWrapper to circumvent the servlet API was doubtful.