Getting Past 403 Forbidden Errors by Enabling Cookies with Python Requests

Encountering 403 Forbidden errors when making requests with the Python Requests library can be frustrating. This article will explain what causes these errors, and how you can resolve them by properly configuring cookies.

What Triggers a 403 Forbidden Error?

A 403 Forbidden client error status response code indicates that the server understands the request but refuses to authorize it. There are a few common triggers for 403 errors:

Out of these common cases, issues with authentication and CSRF tokens most commonly lead to 403 errors with Requests.

Why Do Cookies Matter for Authentication?

Many login mechanisms rely on cookies to store session tokens and authenticate requests. Here is a simplified overview:

1. Client sends login credentials to server
2. Server verifies credentials and creates a session
3. Server sets a session cookie with a token on the client
4. Client sends authenticated requests with the cookie
5. Server validates the session token from the cookie

If cookies are disabled, the client cannot maintain the authenticated session, leading to 403 errors on subsequent requests.

Enabling Cookies with Requests

By default, the Python Requests library will send cookies from the client to the server, but will not save cookies set by the server locally.

To allow cookie persistence on the client, we need to create a Requests Session object and enable cookies:

import requests

session = requests.Session()
session.cookies.set_policy(requests.cookies.DefaultCookiePolicy(strict_rfc2965_unverifiable=True))

Now any cookies set by the server will be stored in the session.cookies object and automatically sent with future requests from this session.

Practical Example with Login

Here is some sample code that logs into a fictional site, stores the authentication cookie, and then accesses a protected resource, avoiding a 403 error:

import requests

session = requests.Session()
session.cookies.set_policy(requests.cookies.DefaultCookiePolicy(strict_rfc2965_unverifiable=True))

# Log in and store session cookie
resp = session.post("https://example.com/login", data={"username": "foo", "password": "bar"})

# Session cookie handles authentication
resp = session.get("https://example.com/private") 
print(resp.text)

So by creating a persistent Session and enabling cookies, we can login once and access authenticated resources without further credentials.

Other Approaches to Avoiding 403 Errors

While cookies are commonly part of authentication schemes, some APIs use token-based authentication instead of sessions:

For these APIs, enabling cookies may not be necessary to avoid 403 errors if you have a valid API token.

Key Takeaways

By understanding the role of cookies in authentication and properly configuring the Requests library, you can resolve frustrating 403 issues when interacting with web APIs and services.