SuperTokens is an open source authentication solution offering features like: Different types of login: Email / password, Passwordless (OTP or Magic link based).

SuperTokens.com

Hi, any guide on how to use Passwordless and Session management in a plain html, js website with flask backend. Is it even possible right now?

Hey! Do you want to use our prebuilt ui or custom UI?

https://github.com/gitcommitshow/supertokens-web-js/tree/master/examples/angular/with-passwordless

Ah, I just realized that there is a recipe provided at https://cdn.jsdelivr.net/gh/supertokens/supertokens-web-js/bundle/passwordless.js for Passwordless. The docs mentioned only three js files, so was unsure where I would get the Passwordless module to use

Hmm. You should checkout the passwordless recipe docs. That should have that link

In the Frontend configuration for Plain JS, it only mentions these three files: 
<script src="https://cdn.jsdelivr.net/gh/supertokens/supertokens-web-js/bundle/website.js"></script>
<script src="https://cdn.jsdelivr.net/gh/supertokens/supertokens-web-js/bundle/supertokens.js"></script>
<script src="https://cdn.jsdelivr.net/gh/supertokens/supertokens-web-js/bundle/session.js"></script>

Ah right. Yea the docs need to be updated for that. We are working on that