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 again, where do I find info about data consistency between databases?
I mean that I've created another database (apart from `supertokens`) which holds some user data.
How do I add users to the new database when a new account has been created?

In our docs, checkout the section for post sign up override

I've read the documentation plus some previous threads and it helped, but still I'm not sure where and how to provide access to my external database in source code in order to connect to it and send data. Should I use SSH Tunnelling or what to make the connection secure?
Also, is it like I should send queries to my DB to make changes to it?

im not really sure about this. If you have a supertokens specfic question,  can help