Can you expand on this? Let's say I want to write a backend with Clojure, wouldn't I still need to write boilerplate for auth, the api endpoints and the CRUD operations?
I'd encourage looking through the documentation for Luminus[1], one framework for writing web apps Clojure, to help you figure out if it suits your personal tolerance for boilerplate. IMO the example for gating API endpoints by authentication[2] is remarkably simple, but you might prefer something more opinionated a la Rails to completely abstract the auth boilerplate away.
For what it's worth, being a lisp, Clojure could certainly support a framework for writing web apps that's highly opinionated, and takes in config for tweaking some defaults (e.g.: auth), thanks to macros.
[1]: https://luminusweb.com/ [2]: https://luminusweb.com/docs/services.html#authentication