🛡️ Fixing ValueError: password cannot be longer than 72 bytes in Python 3.12 / 3.13 (passlib + bcrypt)
When deploying FastAPI authentication routes using passlib[bcrypt] on Python 3.12 or Python 3.13, newer versions of bcrypt (>= 4.1.0) raise:
ValueError: password cannot be longer than 72 bytes, truncate manually if necessary
during passlib's internal detect_wrap_bug startup check.
✅ The Instant Production Fix
Pin bcrypt==4.0.1 alongside passlib[bcrypt] in your requirements.txt:
fastapi
uvicorn
passlib[bcrypt]
bcrypt==4.0.1
python-jose[cryptography]
pydantic[email]
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