Issues in the Existing SecurityMiddleware Code 1. Incorrect use of response.setdefault() instead of response.headers.setdefault() 2. In the process_request() method, HTTPS redirection is done While this works, %-formatting is less readable and slightly less performant than modern alternatives like f-strings 3. Preventing Overwriting of Existing Headers

[Abhijeet Kumar]

1. Incorrect use of response.setdefault() instead of response.headers.setdefault()

Issue:
In the original code, the Cross-Origin-Opener-Policy (COOP) header is set using:

response.setdefault("Cross-Origin-Opener-Policy", self.cross_origin_opener_policy)

This is incorrect because:

1. response.setdefault() does not exist in Django’s HttpResponse class.
2. Headers should be set using response.headers.setdefault() to ensure they are only added if they don’t already exist.

Suggested Modification:
Replace:

response.setdefault("Cross-Origin-Opener-Policy", self.cross_origin_opener_policy)

With:

response.headers.setdefault("Cross-Origin-Opener-Policy", self.cross_origin_opener_policy)

2. Improving String Formatting for Readability & Performance

Issue:
In the process_request() method, HTTPS redirection is done using:

return HttpResponsePermanentRedirect(

"​https://%s%s" % (host, request.get_full_path())

)

While this works, %-formatting is less readable and slightly less performant than modern alternatives like f-strings.

Suggested Modification:
Change:

return HttpResponsePermanentRedirect(

"​https://%s%s" % (host, request.get_full_path())

)

To:
return HttpResponsePermanentRedirect(f"​https://{host}{request.get_full_path()}")

3. Preventing Overwriting of Existing Headers

Issue:

The original code unconditionally sets security headers like:

response.headersStrict-Transport-Security = sts_header
response.headersX-Content-Type-Options = "nosniff"

This could Override existing security policies set by other middleware or custom responses &
Prevent flexibility in modifying security headers dynamically.

Suggested Modification:

Use setdefault() instead of direct assignment:

response.headers.setdefault("Strict-Transport-Security", sts_header)
response.headers.setdefault("X-Content-Type-Options", "nosniff")

Suggested Code:

import re

from django.conf import settings
from django.http import HttpResponsePermanentRedirect
from django.utils.deprecation import MiddlewareMixin

class SecurityMiddleware(MiddlewareMixin):

def init(self, get_response):

super().init(get_response)
self.sts_seconds = settings.SECURE_HSTS_SECONDS
self.sts_include_subdomains = settings.SECURE_HSTS_INCLUDE_SUBDOMAINS
self.sts_preload = settings.SECURE_HSTS_PRELOAD
self.content_type_nosniff = settings.SECURE_CONTENT_TYPE_NOSNIFF
self.redirect = settings.SECURE_SSL_REDIRECT
self.redirect_host = settings.SECURE_SSL_HOST
self.redirect_exempt = [re.compile(r) for r in settings.SECURE_REDIRECT_EXEMPT]
self.referrer_policy = settings.SECURE_REFERRER_POLICY
self.cross_origin_opener_policy = settings.SECURE_CROSS_ORIGIN_OPENER_POLICY

def process_request(self, request):

path = request.path.lstrip("/")
if (

self.redirect
and not request.is_secure()
and not any(pattern.search(path) for pattern in self.redirect_exempt)

):

host = self.redirect_host or request.get_host()
return HttpResponsePermanentRedirect(f"​https://{host}{request.get_full_path()}")

def process_response(self, request, response):

if (

self.sts_seconds
and request.is_secure()
and "Strict-Transport-Security" not in response.headers

):

sts_header = f"max-age={self.sts_seconds}"
if self.sts_include_subdomains:

sts_header += "; includeSubDomains"

if self.sts_preload:

sts_header += "; preload"

response.headers.setdefault("Strict-Transport-Security", sts_header)

if self.content_type_nosniff:

response.headers.setdefault("X-Content-Type-Options", "nosniff")

if self.referrer_policy:

# Support a comma-separated string or iterable of values to allow fallback.
response.headers.setdefault(

"Referrer-Policy",
",".join(

[v.strip() for v in self.referrer_policy.split(",")]
if isinstance(self.referrer_policy, str)
else self.referrer_policy

),

)

if self.cross_origin_opener_policy:

response.headers.setdefault(

"Cross-Origin-Opener-Policy",
self.cross_origin_opener_policy,

)

return response