046-scraping-the-billboard/docs/wiki/Step-2-YouTube-Music-Authentication.md

Step 2 - YouTube Music Authentication

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What the step does

YouTube Music has no simple API key. The ytmusicapi library works by borrowing the login of your browser: you copy the request headers of a logged-in Firefox session once (see Setup and Run), and ytmusicapi browser turns them into browser.json. The program then opens YTMusic("browser.json") and counts your library playlists.

python -m musical_time_machine --check-login

On success it prints Found N playlists in your library. Without a valid browser.json it prints the renewal steps and exits with code 1, instead of a stack trace.

A live run with the author's browser.json (the output shows only the count, never the names of the playlists):

The screenshot shows the run without browser.json and the tests that use a fake YouTube Music.

What we gained

• How cookie-based authentication works. Your browser proves who you are with cookies and headers on every request; copying them lets a script act as that session. That is also why browser.json is a secret, is ignored by git and expires after a while.
• Hiding a library behind a port. The program talks to a MusicService interface; only infrastructure/ytmusic.py imports ytmusicapi. The tests use a fake, and a different music service could replace it.
• Failing helpfully. A missing or expired file becomes a clear message that says how to renew it, because the error a user sees is part of the product.
• A lazy connection. The client is created on first use, so building the service never touches the network.