Hello @lighteye! Thanks for raising the question! We currently use SteemConnect, the most trusted login service on Steem which is also trusted by other Steem dapps like busy.org and SteemMonsters, so it's completely safe to use!
Also, we are going to support login with posting key soon, please stay tuned for that!
Posted using Partiko Android
Looking forward posting key option, @partiko :)