I'm feeling really stupid right now - I'm an experienced javascript & PHP developer but I just can't get my head round this one!
I have developed a system that allows users to create widgets and embed them on their own sites by including one dynamically-generated javascript file. I have now incorporated an authentication system so users of these widgets can register and login on my client's sites. The registration details are stored on my server.
When a user registers or logs in, I was planning on sending back some kind of encrypted token (of their unique ID) so that when they next access a widget on the same site the code will automatically log them in by sending the token to my server and decrypting it.
However, if this token is stored in the browser via localStorage or a cookie, it will be copy-and-paste-able to anyone that can get their hands on it, resulting in them being able to log in as that user. Is there any way I can achieve what I want without this risk?
Thanks in advance!
You can use JWT. Server generates JWT to frontend and when frontend receives JWT it will store it to localstorage. Localstorage is safe place to keep JWT as long as you make sure that user can't perform any XSS on your application.
You can also solve CSRF with JWT if you send it in HTTP header. That makes sure that unauthorized requests won't go through on other domains. You should check this PHP JWT library out. I have used it on my own projects.