Python/Django SameSite cookie middleware and compatibility class

samesite_cookie_compatibility.py

class SameSiteCookieCompatibility:
    """
    Methods to test the user agent and return a bool if is compatible with samesite key in cookie
    https://www.chromium.org/updates/same-site/incompatible-clients
    """

    is_not_compatible: bool = False

    def __init__(self, user_agent) -> None:
        try:
            self.is_not_compatible = self._has_webkit_samesite_bug(
                user_agent
            ) or self._drops_unrecognized_samesite_cookies(user_agent)
        except:
            self.is_not_compatible = True

    def _has_webkit_samesite_bug(self, user_agent) -> bool:
        return (
            (user_agent.os.family == "iOS") and (user_agent.os.version[0] == 12)
        ) or (
            (user_agent.os.family == "Mac OS X")
            and (user_agent.os.version[0] == 10)
            and (user_agent.os.version[1] == 14)
            and (user_agent.browser.family == "Safari")
        )

    def _drops_unrecognized_samesite_cookies(self, user_agent) -> bool:
        if user_agent.browser.family == "UC Browser":
            return not self._is_browser_version_at_least(12, 13, 2, user_agent)
        return (
            (user_agent.browser.family == "Chrome")
            and self._is_browser_version_at_least(51, 0, 0, user_agent)
            and not self._is_browser_version_at_least(67, 0, 0, user_agent)
        )

    def _is_browser_version_at_least(self, major: int, minor: int, build: int, user_agent) -> bool:
        major_version, minor_version, build_version = user_agent.browser.version
        if major_version != major:
            return major_version > major
        if minor_version != minor:
            return minor_version > minor
        return build_version >= build

samesite_cookie_middleware.py

import user_agents
from .samesite_cookie_compatibility import SameSiteCookieCompatibility

class ExampleCookieMiddleware:

    def __init__(self, get_response=None):
        self.get_response = get_response

    def __call__(self, request):
        response = self.get_response(request)
        response.set_cookie(key="key", value="value") # example

        # Add "SameSite" and "secure" cookie keys for Chrome 80, only for compatible browsers (https://www.chromium.org/updates/same-site)
        ua_string: str = request.META.get("HTTP_USER_AGENT", "")
        user_agent = user_agents.parse(ua_string)
        if not SameSiteCookieCompatibility(user_agent).is_not_compatible:
            response.cookies["key"]["samesite"] = "None"
            response.cookies["key"]["secure"] = True

        return response