Keila VS guardian

Keila is another one with similar features plus a visual (block) editor for designing the email template/content: https://github.com/pentacent/keila

Someone on r/selfhosted built an alternative for Mailchimp called Keila a while ago. (https://github.com/pentacent/keila). I haven't tried it myself but this sounds promising. You can use your own mailserver with it (which I recommend you do not selfhost for business purposes). As it is licensed right now, it should be way cheaper to use this instead of Mailchimp.

If that doesn’t fix it, please feel free to post a bug report with more details here: https://github.com/pentacent/keila/issues

I've used Keila in the past and was pretty happy w/ it.

What about keila (https://github.com/pentacent/keila) I haven't used it myself yet..

A cool feature that’s not quite ready yet but that I’m working on at the moment is the ability to add custom campaign data. This will allow you to create a template (e.g. for showing your most recent blog posts) and feed it with data via the API - giving you the easiest fully-automated email campaigns ever. I wrote a little thread over at Twitter about this (Draft PR on GitHub). I’m curious to hear if/how you’d use that feature!

As for the original question, OP you should check out https://github.com/ueberauth/guardian if you want to roll your own auth. If not rolling you own you can just use a standard Oauth provider and validate their tokens (surprise they are JWTs) in you backend using their public keys.

AuthN: For authentication, I'd look at the built-in auth generator. If you need to add JWT things, joken and/or guardian can probably meet your needs.