In more "formal" discussion environments than an Internet discussion thread, sometimes a "proposal" or statement made by someone will be met by someone else giving their support of said statement by stating "I second that", meaning they're the second person in the room to support the statement verbally aloud.
TLDR; They're throwing their support of the OP's statement into the ring.
> "do you mean authentik is much easier to setup?"
I do believe from the context of the rest of their comment that's exactly what they mean to say.
