feat(logger): introduce user configurable logger

[balazsorban44]

What:

Let the user configure logging.

Why:

This lets the user override certain log levels, in case they would like to forward the log messages to something else than console.

How:

Adds a new option to NextAuth, called logger.

It has three properties, error, warn and debug. Those not overridden will fall back to the basic logger function.

To cover client-side logs, we do make the assumption that your 3rd party logger does not support client-side logging. To mitigate this, we proxy all client-side log events to an endpoint (/api/auth/_log) that sends those further to your custom logger config.

We use sendBeacon if available.

Checklist:

• Documentation
• Tests (locally)
• Ready to be merged
  

closes #869
closes #907

continuation of #870, #1090 (cannot git 🙈)

[vercel]

This pull request is being automatically deployed with Vercel (learn more).
To see the status of your deployment, click below or on the icon next to each commit.

🔍 Inspect: https://vercel.com/nextauthjs/next-auth/2bw7uq44z
✅ Preview: https://next-auth-git-feature-improve-logging.nextauthjs.vercel.app

[ndom91]

This looks awesome! Good docs example as well 👍

[github-actions]

🎉 This PR is included in version 3.4.0 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

Your semantic-release bot 📦🚀