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

SuperTokens.com

Hello, trying to implement `ThirdPartyEmailPassword` recipe for the following template which uses Next.js: https://github.com/devias-io/material-kit-react

Here I'd like to use the custom login/register UI provided by the template, which has two different pages for signin and signup (`login.js` , `register.js`)
under the `/auth` directory. Can someone please help me out on how to implement this or direct me to an example of Next.js integration with custom login UI?

in this case, you should not use our pre built UI. Checkout the section of using your own UI in our docs

and essentially, you want to use supertokens-web-js instead of supertokens-auth-react (which is explained in the use your own UI section)