In the documentation for lumberjack output, under the ssl_certificate setting it just says, "This is a required setting" and "ssl certificate to use."
My questions are: what is this certificate used for, and why is it required? How do I perform client authentication, assuming this is not already being performed?
Note: I am sending logs from one logstash (client) to another (server). My server side is a beats input with no CA's specified and ssl_verify_mode => "none". When I tried adding the CA and specifying ssl_verify_mode to force_peer it did not work.