AFAIK HSTS is a server side property that tells the browser that is should only work with https request with this server (correct me please if I'm wrong).
HSTS will not help in cases of redirecting from http to https, in this time frame of redirection MIM attack can happen, unless you site listed on the browser HSTS list.
If I have a server that only get requests from libcurl do I need to support HSTS? Will it have any meaning? Does libcurl also supports HSTS and will works only with https sites after receiving this param from the server?