How to Fix Cookie Issues Through Proxy

Cookies are one of the most common sources of errors when working with proxies. Sessions break, authentication fails, data is lost. In this article, we'll figure out why this happens and how to properly configure cookie handling for stable operation.

Why cookies are lost when using a proxy

When you send a request through a proxy, an intermediate node stands between your client and the target server. This creates several problems:

• Different IP addresses for one session. The server may notice that requests come from different addresses and reject cookies as suspicious.
• Loss of Set-Cookie headers. Incorrect proxy configuration may not transmit Set-Cookie headers to the client.
• Domain and path mismatch. If the proxy rewrites the Host header, cookies may not be saved due to domain mismatch.
• Lack of state persistence. If you send each request separately without saving cookies, the session will be lost.

What is a cookie jar and how to use it

A cookie jar is a storage for cookies that automatically manages their sending and receiving. Instead of manually adding Cookie headers to each request, you let the library do it automatically.

Most HTTP clients have built-in cookie jar support:

import requests
from requests.cookies import RequestsCookieJar

# Create a jar for storing cookies
jar = RequestsCookieJar()

# First request — server will send Set-Cookie
response1 = requests.get(
    'https://example.com/login',
    cookies=jar,
    proxies={'https': 'http://proxy.example.com:8080'}
)

# Cookies are automatically saved to jar
print(jar)

# Second request — cookies will be sent automatically
response2 = requests.get(
    'https://example.com/dashboard',
    cookies=jar,
    proxies={'https': 'http://proxy.example.com:8080'}
)

Without a jar, you would have to manually parse Set-Cookie and add them to the next request — this is unreliable and cumbersome.

Saving cookies between requests

If your script runs for a long time or you need to restore a session after a restart, save cookies to a file:

import requests
from http.cookiejar import LWPCookieJar

# Create a jar with file persistence
jar = LWPCookieJar('cookies.txt')

# Load old cookies if they exist
try:
    jar.load(ignore_discard=True, ignore_expires=True)
except FileNotFoundError:
    pass

# Use jar in requests
response = requests.get(
    'https://example.com/login',
    cookies=jar,
    proxies={'https': 'http://proxy.example.com:8080'}
)

# Save updated cookies
jar.save(ignore_discard=True, ignore_expires=True)

The ignore_discard=True and ignore_expires=True flags allow you to save even temporary cookies.

Cookie domain binding issues

Cookies have a Domain attribute that determines which domains they will be sent to. Problems arise if:

• Proxy rewrites the Host. If the proxy changes the Host header, the cookie jar may reject the cookie as belonging to a different domain.
• Subdomains don't match. A cookie for example.com may not be sent to api.example.com.
• Path doesn't match. A cookie for /api will not be sent to /admin.

Check cookie attributes like this:

import requests

response = requests.get(
    'https://example.com',
    proxies={'https': 'http://proxy.example.com:8080'}
)

# Print all cookies
for cookie in response.cookies:
    print(f"Name: {cookie.name}")
    print(f"Value: {cookie.value}")
    print(f"Domain: {cookie.domain}")
    print(f"Path: {cookie.path}")
    print(f"Secure: {cookie.secure}")
    print(f"HttpOnly: {cookie.has_nonstandard_attr('HttpOnly')}")
    print("---")

If the Domain is too narrow, try explicitly specifying cookies instead of automatic management:

headers = {
    'Cookie': 'session_id=abc123; user_token=xyz789'
}

response = requests.get(
    'https://example.com/api',
    headers=headers,
    proxies={'https': 'http://proxy.example.com:8080'}
)

Secure and HttpOnly flags

The Secure flag means the cookie is only sent over HTTPS. If you're using an HTTP proxy to access an HTTPS resource, make sure the connection to the proxy is protected or that the proxy correctly tunnels HTTPS.

The HttpOnly flag prevents access to the cookie from JavaScript. This doesn't affect sending the cookie in requests, but it's important to remember that you won't be able to read such cookies from the browser.

When working with residential proxies, make sure that:

• The proxy supports HTTPS (CONNECT method)
• Certificates are valid (don't use verify=False in production)
• Headers are not rewritten by the proxy

Practical code examples

Example 1: Login with session preservation

import requests
from requests.cookies import RequestsCookieJar

jar = RequestsCookieJar()
proxy = 'http://proxy.example.com:8080'

# Login
login_response = requests.post(
    'https://example.com/login',
    data={'username': 'user', 'password': 'pass'},
    cookies=jar,
    proxies={'https': proxy}
)

if login_response.status_code == 200:
    print("Login successful")
    
    # Use saved session
    dashboard = requests.get(
        'https://example.com/dashboard',
        cookies=jar,
        proxies={'https': proxy}
    )
    print(dashboard.text)

Example 2: Processing multiple requests

import requests
from http.cookiejar import LWPCookieJar
import time

jar = LWPCookieJar('session.txt')
try:
    jar.load(ignore_discard=True)
except:
    pass

proxy = 'http://proxy.example.com:8080'
urls = [
    'https://example.com/page1',
    'https://example.com/page2',
    'https://example.com/page3'
]

for url in urls:
    response = requests.get(
        url,
        cookies=jar,
        proxies={'https': proxy},
        timeout=10
    )
    print(f"{url}: {response.status_code}")
    jar.save(ignore_discard=True)
    time.sleep(1)  # Don't overload the server

Example 3: Explicit cookie passing when issues occur

import requests

proxy = 'http://proxy.example.com:8080'

# If automatic management doesn't work
cookies_dict = {
    'session_id': 'abc123def456',
    'user_pref': 'dark_mode'
}

headers = {
    'User-Agent': 'Mozilla/5.0...',
    'Cookie': '; '.join([f"{k}={v}" for k, v in cookies_dict.items()])
}

response = requests.get(
    'https://example.com/api/data',
    headers=headers,
    proxies={'https': proxy}
)

print(response.json())

Debugging cookie issues

If cookies aren't working, use these tools:

Enable logging for debugging:

import logging
import requests

logging.basicConfig(level=logging.DEBUG)

# Now all requests will output headers and cookies
response = requests.get(
    'https://example.com',
    proxies={'https': 'http://proxy.example.com:8080'}
)

Check that the proxy doesn't block cookies:

curl -v -x http://proxy.example.com:8080 https://example.com

# Look at the headers:
# Set-Cookie: ... (should be present)
# Cookie: ... (should be sent in the next request)

Summary

Cookie issues when working through a proxy are solved with proper configuration:

• Use a cookie jar for automatic cookie management
• Save cookies between requests to a file
• Check domain binding and Path attributes
• Ensure HTTPS support in the proxy
• Use debugging to identify issues

For automation and scraping tasks that require reliable session handling through a proxy, residential proxies with HTTPS support and cookie management are suitable. Start with a simple cookie jar and move to more complex schemes only if needed.