AFAIK, the answer is no, currently, there's no way to encrypt rpc requests
if not using kerberos. There were some discussions about it in HBASE-26548
<https://issues.apache.org/jira/browse/HBASE-26548> and on this slack thread
<https://apache-hbase.slack.com/archives/C13K8NVAM/p1638980520110600>. The
patch in HBASE-26548 is a very rough PoC taking advantage of netty TLS
capabilities, and hardcoding it in the netty RPC layer. Can be used as a
reference, or refined further to a point where it would be merge ready, if
you are interested in investing some effort on this.
