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CRUNCHYROLL DOWNLOADER - CHALLENGE 2 SOLUTION
Chapter 3: JWT Login & Authentication
Challenge: Token Caching
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PROBLEM:
Implement save_token() and load_cached_token() to avoid re-logging in.

SOLUTION:
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File: crunchyroll_utils.py (token caching)

import json
from pathlib import Path
from datetime import datetime

def save_token(token: str, cache_file: str):
    """Save JWT token to file for reuse."""

    print(f"💾 Saving token to cache...")

    data = {
        "token": token,
        "timestamp": datetime.now().isoformat(),
        "note": "Do not commit this file to Git!"
    }

    try:
        with open(cache_file, 'w') as f:
            json.dump(data, f, indent=2)
        print(f"✅ Token cached to {cache_file}")
        return True
    except Exception as e:
        print(f"❌ Error saving token: {e}")
        return False


def load_cached_token(cache_file: str) -> str:
    """Load cached JWT token if it exists."""

    cache_path = Path(cache_file)

    # Check if cache file exists
    if not cache_path.exists():
        print(f"ℹ️  No cached token found")
        return None

    try:
        with open(cache_file, 'r') as f:
            data = json.load(f)

        token = data.get("token")
        saved_at = data.get("timestamp")

        if token:
            print(f"✅ Loaded cached token")
            if saved_at:
                print(f"   Saved at: {saved_at}")
            return token
        else:
            print(f"❌ No token in cache file")
            return None

    except json.JSONDecodeError:
        print(f"❌ Cache file corrupted (invalid JSON)")
        return None
    except Exception as e:
        print(f"❌ Error loading token: {e}")
        return None


WHY TOKEN CACHING?
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WITHOUT caching:
- Every run: Login → Get token → Use it
- Slow (login request takes time)
- More requests to server
- User sees login delay

WITH caching:
- First run: Login → Save token → Use it
- Later runs: Load token → Use it (no login!)
- Fast (skip login step)
- Fewer server requests
- Better user experience


HOW IT WORKS
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First Run:
┌─────────────────────────────────────────┐
│ 1. User runs: python download.py        │
│ 2. Check for token_cache.json - NO      │
│ 3. Must login (username/password)       │
│ 4. Get JWT token from server            │
│ 5. Save token to token_cache.json       │
│ 6. Use token to fetch episodes          │
└─────────────────────────────────────────┘
              ↓
        (takes ~5 seconds)

Second Run (same day):
┌─────────────────────────────────────────┐
│ 1. User runs: python download.py        │
│ 2. Check for token_cache.json - YES!    │
│ 3. Load token from file                 │
│ 4. Use token to fetch episodes          │
│ 5. Done! (skip login)                   │
└─────────────────────────────────────────┘
              ↓
        (takes ~1 second!)


CACHE FILE FORMAT
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token_cache.json:

{
  "token": "eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9...",
  "timestamp": "2026-06-30T12:34:56.789012",
  "note": "Do not commit this file to Git!"
}


USAGE IN MAIN SCRIPT
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from config import Config
from crunchyroll_utils import login, load_cached_token, save_token

config = Config()
if not config.validate():
    exit(1)

# Try to load cached token
token = load_cached_token(config.token_cache)

# If no cache, login
if not token:
    print("🔐 No cached token, logging in...")
    token = login(config)
    if not token:
        exit(1)
    # Save it for next time
    save_token(token, config.token_cache)

# Now use token for API requests
print("✅ Ready to fetch episodes!")


WHEN CACHE EXPIRES
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JWT tokens have expiration (usually 1 hour or 1 day)

If you get 401 error:
- Token expired
- Delete token_cache.json
- Re-run script (will login again)

Example:
❌ 401 Unauthorized
→ Delete token_cache.json
→ python download.py
→ ✅ Re-login, save new token

This is automatic handling of token refresh!


SECURITY NOTE
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⚠️ IMPORTANT:
- token_cache.json contains your JWT token
- It's like a temporary password file
- Must be in .gitignore (don't commit!)
- If someone gets it, they can access your account
- Tokens expire anyway (1 hour/1 day)
- If compromised, just delete it and re-login

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