{"slug": "fastapi-for-ai-engineers-part-6-jwt-authentication-in-fastapi", "title": "FastAPI for AI Engineers - Part 6: JWT Authentication in FastAPI", "summary": "A developer demonstrates how to implement JWT authentication in FastAPI for AI applications, covering password hashing with bcrypt and token generation using python-jose. The tutorial includes registration and login endpoints, emphasizing secure credential storage and token-based access control.", "body_md": "In the previous article, we explored the concepts of Authentication and Authorization.\n\nWe learned that:\n\nUnderstanding the concepts is important, but real-world applications require actual implementation.\n\nIf you've ever used Gmail, LinkedIn, GitHub, or ChatGPT, you've already used authentication systems countless times.\n\nYou enter your username and password, the application verifies your identity, and you gain access to protected resources.\n\nBut how does this actually work behind the scenes?\n\nIn this article, we'll build a complete JWT Authentication system using FastAPI.\n\nIf you haven't read the previous article, check it out first:\n\nImagine building an AI-powered learning platform.\n\nWithout authentication:\n\nClearly, this is a security problem.\n\nApplications need a way to:\n\nThis is where JWT Authentication comes in.\n\nJWT stands for **JSON Web Token**.\n\nA JWT is a secure token that contains information about a user.\n\nInstead of sending a username and password with every request, the user sends a token.\n\nTypical flow:\n\n```\nRegister User\n      ↓\n   Login\n      ↓\nVerify Credentials\n      ↓\nGenerate JWT Token\n      ↓\nAccess Protected Routes\npip install python-jose passlib[bcrypt]\n```\n\nWe'll use:\n\n`passlib`\n\nfor password hashing`python-jose`\n\nfor JWT token generation and verificationStoring passwords in plain text is extremely dangerous.\n\nNever do this:\n\n```\nusers = {\n    \"rahul\": \"password123\"\n}\n```\n\nIf the database is compromised, every user's password becomes visible.\n\nInstead, we store a hashed version.\n\n``` python\nfrom passlib.context import CryptContext\n\npwd_context = CryptContext(\n    schemes=[\"bcrypt\"],\n    deprecated=\"auto\"\n)\n```\n\n`CryptContext`\n\nmanages password hashing algorithms.\n\nIn this example:\n\n```\nschemes=[\"bcrypt\"]\n```\n\nwe tell FastAPI to use the bcrypt hashing algorithm.\n\n```\nhashed_password = pwd_context.hash(\"password123\")\n\nprint(hashed_password)\n```\n\nOutput:\n\n```\n$2b$12$.....\n```\n\nNotice that the original password is no longer visible.\n\nWhen the user logs in:\n\n```\npwd_context.verify(\n    \"password123\",\n    hashed_password\n)\n```\n\nreturns:\n\n```\nTrue\n```\n\nThis allows us to verify passwords without storing them in plain text.\n\nLet's create a simple registration endpoint.\n\n``` python\nfrom fastapi import FastAPI\n\napp = FastAPI()\n\nusers = {}\n\n@app.post(\"/register\")\ndef register(username: str, password: str):\n\n    hashed_password = pwd_context.hash(password)\n\n    users[username] = hashed_password\n\n    return {\"message\": \"User registered successfully\"}\n```\n\nNow let's verify credentials.\n\n``` python\n@app.post(\"/login\")\ndef login(username: str, password: str):\n\n    stored_password = users.get(username)\n\n    if not stored_password:\n        return {\"message\": \"User not found\"}\n\n    if not pwd_context.verify(password, stored_password):\n        return {\"message\": \"Invalid credentials\"}\n\n    return {\"message\": \"Login successful\"}\n```\n\nAt this point, users can log in successfully.\n\nHowever, they still need to send their username and password with every request.\n\nJWT solves this problem.\n\n``` python\nfrom jose import jwt\nfrom datetime import datetime, timedelta\n\nSECRET_KEY = \"mysecretkey\"\n\nALGORITHM = \"HS256\"\n```\n\nThe secret key is used to sign tokens.\n\nIf someone modifies the token, the signature becomes invalid.\n\n``` python\ndef create_access_token(data: dict):\n\n    to_encode = data.copy()\n\n    expire = datetime.utcnow() + timedelta(minutes=30)\n\n    to_encode.update({\"exp\": expire})\n\n    encoded_jwt = jwt.encode(\n        to_encode,\n        SECRET_KEY,\n        algorithm=ALGORITHM\n    )\n\n    return encoded_jwt\npython\n@app.post(\"/login\")\ndef login(username: str, password: str):\n\n    stored_password = users.get(username)\n\n    if not stored_password:\n        return {\"message\": \"User not found\"}\n\n    if not pwd_context.verify(password, stored_password):\n        return {\"message\": \"Invalid credentials\"}\n\n    token = create_access_token(\n        {\"sub\": username}\n    )\n\n    return {\n        \"access_token\": token,\n        \"token_type\": \"bearer\"\n    }\n```\n\nSuccessful login now returns:\n\n```\n{\n  \"access_token\": \"eyJhbGciOiJIUzI1NiIs...\",\n  \"token_type\": \"bearer\"\n}\n```\n\nNow we can protect routes.\n\n``` python\n@app.get(\"/profile\")\ndef get_profile():\n\n    return {\n        \"message\": \"Protected profile data\"\n    }\n```\n\nCurrently anyone can access it.\n\nIn production applications, FastAPI verifies the JWT token before allowing access.\n\nWe'll implement complete route protection in the next article.\n\nFor now, focus on understanding:\n\nThese form the foundation of every authentication system.\n\n```\nRegister User\n      ↓\nHash Password\n      ↓\nStore Hash\n      ↓\n   Login\n      ↓\nVerify Password\n      ↓\nGenerate JWT\n      ↓\nAccess Protected Routes\n```\n\nToday we built the core components of JWT Authentication:\n\nA user can now register, log in, and receive a signed JWT token.\n\nHowever, generating a token is only half the story.\n\nThe next step is learning how to validate tokens and protect routes using FastAPI dependencies.\n\nIn the next article, we'll implement JWT-based route protection and begin exploring Role-Based Access Control (RBAC).", "url": "https://wpnews.pro/news/fastapi-for-ai-engineers-part-6-jwt-authentication-in-fastapi", "canonical_source": "https://dev.to/zeroshotanu/fastapi-for-ai-engineers-part-6-jwt-authentication-in-fastapi-5fpk", "published_at": "2026-06-15 17:22:40+00:00", "updated_at": "2026-06-15 17:36:29.718712+00:00", "lang": "en", "topics": 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