[enh] uses caching for hash to avoid heavy recalculation and process spawning

helpers.lua

@@ -72,6 +72,9 @@ end
 
 -- Hash a string using hmac_sha512, return a hexa string
 function hmac_sha512(key, message)
+    local cache_key = key..":"..message
+
+    if not cache:get(cache_key) then
         -- lua ecosystem is a disaster and it was not possible to find a good
         -- easily multiplatform integrable code for this
         -- Python has this buildin, so we call it directly
@@ -88,7 +91,12 @@ function hmac_sha512(key, message)
         -- so we need to remove the "(stdin)= " at the beginning
         local hash = pipe:read():sub(string.len("(stdin)= ") + 1)
         pipe:close()
+
+        cache:set(cache_key, hash, conf["session_timeout"])
         return hash
+    else
+        return cache:get(cache_key)
+    end
 end