So I am creating a website to learn some PHP/Javascript/HTML/CSS and so on and I ran into a problem to which I can't come up with a solution. So basically I have regular login form using PHP which uses POST to send the data and authenticate. I also want to integrate external Twitch.tv OAuth2 authentication.
By using normal PHP login I store my information inside PostgreSQL database using php. I want to do something similar using OAuth2. For example store Twitch.tv name as a username inside the database and token as a password.
The problem is that the external authentication I am using is based on their Javascript API and it stores the information inside the DOM storage which I found is unable to be access by using PHP. The redirect_uri with a token is also a fragment which can't be retrieved by PHP.
Should I just scrap the JS part and try doing it entirely in PHP?
Side question: I checked other website which also uses Twitch authentication and it uses these callback links "https://api.nightbot.tv/auth/twitch/callback?code=****". What exactly are these callbacks?