[Minor] Simplify auth=pass generation of AR/AAR header

lualib/lua_auth_results.lua

@@ -171,25 +171,16 @@ local function gen_auth_results(task, settings)
   local smtp_from = task:get_from('smtp')
 
   if u and smtp_from then
-    local hdr
-
-    if #smtp_from[1]['addr'] > 0 then
-      if settings['add_smtp_user'] then
-        hdr = string.format('auth=pass smtp.auth=%s smtp.mailfrom=%s',
-          u, smtp_from[1]['addr'])
-      else
-        hdr = string.format('auth=pass smtp.mailfrom=%s',
-          smtp_from[1]['addr'])
-      end
-    else
-      if settings['add_smtp_user'] then
-        hdr = string.format('auth=pass smtp.auth=%s', u)
-      else
-        hdr = 'auth=pass'
-      end
+    local hdr = {[1] = 'auth=pass'}
+
+    if settings['add_smtp_user'] then
+      table.insert(hdr,'smtp.auth=' .. u)
+    end
+    if smtp_from[1]['addr'] then
+      table.insert(hdr,'smtp.mailfrom=' .. smtp_from[1]['addr'])
     end
 
-    table.insert(hdr_parts, hdr)
+    table.insert(hdr_parts, table.concat(hdr,' ')
   end
 
   if #hdr_parts > 0 then