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12 min readNgusa

Implementing Secure JWT Authentication in Backend APIs

Authentication is critical for any backend application. Here's how to implement secure JWT-based authentication with best practices.

JWT Authentication Flow

  • User logs in with credentials
  • Server validates and returns JWT access token + refresh token
  • Client includes token in subsequent requests
  • Server validates token and processes request

Implementation with FastAPI

Password Hashing

python
from passlib.context import CryptContext

pwd_context = CryptContext(schemes=["bcrypt"], deprecated="auto")

def hash_password(password: str) -> str:
    return pwd_context.hash(password)

def verify_password(plain: str, hashed: str) -> bool:
    return pwd_context.verify(plain, hashed)

Token Generation

python
from jose import jwt
from datetime import datetime, timedelta

def create_access_token(data: dict):
    to_encode = data.copy()
    expire = datetime.utcnow() + timedelta(minutes=15)
    to_encode.update({"exp": expire})
    return jwt.encode(to_encode, SECRET_KEY, algorithm="HS256")

def create_refresh_token(data: dict):
    to_encode = data.copy()
    expire = datetime.utcnow() + timedelta(days=7)
    to_encode.update({"exp": expire})
    return jwt.encode(to_encode, SECRET_KEY, algorithm="HS256")

Protected Routes

python
from fastapi import Depends, HTTPException
from fastapi.security import HTTPBearer

security = HTTPBearer()

async def get_current_user(token: str = Depends(security)):
    try:
        payload = jwt.decode(token.credentials, SECRET_KEY)
        return payload
    except JWTError:
        raise HTTPException(status_code=401, detail="Invalid token")

Security Best Practices

  • Short-lived Access Tokens - 15-30 minutes maximum
  • HTTP-only Cookies - Store tokens securely
  • HTTPS Only - Never transmit tokens over HTTP
  • Token Rotation - Refresh tokens regularly
  • Blacklisting - Implement token revocation

Refresh Token Strategy

Store refresh tokens in database with:

  • User association
  • Expiration date
  • Device/IP information
  • Revocation status

Conclusion

Proper JWT implementation with refresh tokens, password hashing, and security best practices is essential for building secure backend APIs.

References & Further Reading

    Implementing Secure JWT Authentication in Backend APIs | Samwel Ngusa