set session cookie with expiration date and secure flag

app.lua

@@ -1,4 +1,5 @@
 local lapis = require("lapis")
+local date = require("date")
 local app = lapis.Application()
 local constants = require("constants")
 local babycode = require("lib.babycode")
@@ -14,6 +15,13 @@ local util = require("util")
 app:enable("etlua")
 app.layout = require "views.base"
 
+app.cookie_attributes = function (self, name, value)
+  if name == config.session_name then
+    local expires = date(true):adddays(30):fmt("${http}")
+    return "Expires="..expires.."; Path=/; HttpOnly; Secure"
+  end
+end
+
 local function inject_constants(req)
   req.constants = constants
   math.randomseed(os.time())