I really wish there was such an easy off-the shelf auth solution for Go
There are solutions out there for golang (FusionAuth, my employer, is one) but I think you are looking for one that integrates directly into an application the way that better-auth does (just like devise for rails, or Django's user model).
I'm not aware of any such library for golang. This reddit thread might be helpful: https://www.reddit.com/r/golang/comments/1le9q65/is_there_a_... with some options to evaluate.