I’m working on a FastAPI application that uses Jinja2 for rendering templates and I’m struggling with the correct way to implement CSRF protection. Right now I have the SessionMiddleware set up like this:
from fastapi import FastAPI
from starlette.middleware.sessions import SessionMiddleware
my_app = FastAPI()
my_app.add_middleware(SessionMiddleware, secret_key="my-secret-key-here")
But I’m not sure if my approach is right. Here’s what I’m currently doing:
- Generate a random token and store it in the user session
- Send this token to my Jinja2 templates through context data
- Add the token as a header when making POST requests
- Create custom middleware to verify the header token matches what’s stored in session
I know there are external packages available but they seem to do similar things to what I’ve already built. The docs I’ve found don’t really explain how to pass the CSRF token to templates so I’m wondering if there’s some automatic handling I’m missing.
What’s the recommended approach for handling CSRF tokens with FastAPI and Jinja2? Am I on the right track or should I be doing this differently?
honestly fastapi-csrf-protect package saves alot of headache here. just pip install it and you get proper token generation plus built-in jinja2 integration. way easier than reinventing the wheel imo, especially when dealing with double-submit cookie patterns or ajax requests
I ran into similar issues when implementing CSRF protection in my FastAPI project last year. One approach that worked well for me was creating a dependency function that handles both token generation and validation. You can use Depends() to inject the CSRF functionality into your route handlers, which keeps the logic clean and reusable. For the Jinja2 side, I ended up writing a simple function that automatically adds the token to the template context - this way you don’t have to remember to include it manually in every route. The key insight I discovered is that you need to ensure your token generation uses cryptographically secure random values, so secrets.token_urlsafe() is preferable over basic random functions. Also worth noting that if you’re using AJAX requests, you’ll want to expose the token through a meta tag in your HTML head section so JavaScript can easily access it. This approach has been running in production for months without issues and feels more Pythonic than rolling custom middleware.
Your implementation sounds solid but there’s actually a more streamlined approach. Instead of custom middleware, consider using python-multipart with form data rather than headers. When handling POST requests, include the CSRF token as a hidden form field and validate it server-side before processing. I’ve found that storing the token in session works well, but generating it per-session rather than per-request reduces complexity while maintaining security. In your Jinja2 context processor, you can automatically inject the CSRF token into all templates so you don’t have to manually pass it every time. One thing to watch out for - make sure you’re comparing tokens using a constant-time comparison function to prevent timing attacks. The secrets.compare_digest() function works perfectly for this. Also, consider setting appropriate SameSite cookie attributes on your session cookies for additional protection against cross-site attacks.