Enable the site-wide cache. If these are enabled, each Django-powered page will be cached for as long as the
CACHE_MIDDLEWARE_SECONDS setting defines. See the cache documentation.
Adds a few conveniences for perfectionists:
- Forbids access to user agents in the
DISALLOWED_USER_AGENTSsetting, which should be a list of compiled regular expression objects.
- Performs URL rewriting based on the
Trueand the initial URL doesn’t end with a slash, and it is not found in the URLconf, then a new URL is formed by appending a slash at the end. If this new URL is found in the URLconf, then Django redirects the request to this new URL. Otherwise, the initial URL is processed as usual.For example,
foo.com/barwill be redirected to
foo.com/bar/if you don’t have a valid URL pattern for
foo.com/barbut do have a valid pattern for
True, URLs that lack a leading www. will be redirected to the same URL with a leading www.
Both of these options are meant to normalize URLs. The philosophy is that each URL should exist in one, and only one, place. Technically a URL
foo.com/baris distinct from
foo.com/bar/– a search-engine indexer would treat them as separate URLs – so it’s best practice to normalize URLs.
- Handles ETags based on the
USE_ETAGSis set to
True, Django will calculate an ETag for each request by MD5-hashing the page content, and it’ll take care of sending
Not Modifiedresponses, if appropriate.
CommonMiddlewareand override the attribute to customize the redirects issued by the middleware.
django.middleware.common.BrokenLinkEmailsMiddleware.Sends broken link notification emails to
Compresses content for browsers that understand GZip compression (all modern browsers).
This middleware should be placed before any other middleware that need to read or write the response body so that compression happens afterward.
It will NOT compress content if any of the following are true:
- The content body is less than 200 bytes long.
- The response has already set the
- The request (the browser) hasn’t sent an
You can apply GZip compression to individual views using the
Conditional GET Middleware
Handles conditional GET operations. If the response has a
Last-Modified header, and the request has
If-Modified-Since, the response is replaced by an
Also sets the
Enables language selection based on data from the request. It customizes content for each user. See the internationalization documentation.
LocaleMiddleware.response_redirect_class defaults to
LocaleMiddleware and override the attribute to customize the redirects issued by the middleware.
Enables cookie- and session-based message support. See the messages documentation.
django.middleware.security.SecurityMiddleware provides several security enhancements to the request/response cycle. The
SecurityMiddleware achieves this by passing special headers to the browser. Each one can be independently enabled or disabled with a setting.
HTTP Strict Transport Security
For sites that should only be accessed over HTTPS, you can instruct modern browsers to refuse to connect to your domain name via an insecure connection (for a given period of time) by setting the
Strict-Transport-Security header. This reduces your exposure to some SSL-stripping man-in-the-middle (MITM) attacks.
SecurityMiddleware will set this header for you on all HTTPS responses if you set the
SECURE_HSTS_SECONDS setting to a non-zero integer value.
When enabling HSTS, it’s a good idea to first use a small value for testing, for example,
SECURE_HSTS_SECONDS = 3600 for one hour. Each time a Web browser sees the HSTS header from your site, it will refuse to communicate non-securely (using HTTP) with your domain for the given period of time.
Once you confirm that all assets are served securely on your site (i.e. HSTS didn’t break anything), it’s a good idea to increase this value so that infrequent visitors will be protected (31536000 seconds, i.e. 1 year, is common).
Additionally, if you set the
SECURE_HSTS_INCLUDE_SUBDOMAINS setting to
SecurityMiddleware will add the
includeSubDomains tag to the
Strict-Transport-Security header. This is recommended (assuming all sub-domains are served exclusively using HTTPS), otherwise your site may still be vulnerable via an insecure connection to a sub-domain.
Some browsers will try to guess the content types of the assets that they fetch, overriding the
Content-Type header. While this can help display sites with improperly configured servers, it can also pose a security risk.
To prevent the browser from guessing the content type and force it to always use the type provided in the
Content-Type header, you can pass the
X-Content-Type-Options: nosniff header.
SecurityMiddleware will do this for all responses if the
SECURE_CONTENT_TYPE_NOSNIFF setting is
Note that in most deployment situations where Django isn’t involved in serving user-uploaded files, this setting won’t help you. For example, if your
MEDIA_URL is served directly by your front-end Web server (nginx, Apache, etc.) then you’d want to set this header there.
On the other hand, if you are using Django to do something like require authorization in order to download files and you cannot set the header using your Web server, this setting will be useful.
X-XSS-Protection header is used to control the operation of the XSS filter.
To enable the XSS filter in the browser, and force it to always block suspected XSS attacks, you can pass the
X-XSS-Protection: 1; mode=block header.
SecurityMiddleware will do this for all responses if the
SECURE_BROWSER_XSS_FILTER setting is
If your site offers both HTTP and HTTPS connections, most users will end up with an unsecured connection by default. For best security, you should redirect all HTTP connections to HTTPS.
If you set the
SECURE_SSL_REDIRECT setting to True,
SecurityMiddleware will permanently (HTTP 301) redirect all HTTP connections to HTTPS.
For performance reasons, it’s preferable to do these redirects outside of Django, in a front-end load balancer or reverse-proxy server such as nginx.
SECURE_SSL_REDIRECT is intended for the deployment situations where this isn’t an option.
SECURE_SSL_HOST setting has a value, all redirects will be sent to that host instead of the originally-requested host.
If there are a few pages on your site that should be available over HTTP, and not redirected to HTTPS, you can list regular expressions to match those URLs in the
If you are deployed behind a load-balancer or reverse-proxy server and Django can’t seem to tell when a request actually is already secure, you may need to set the
Enables session support. See Chapter 15 for more information.
attribute representing the current site to every incoming
HttpRequest object. See the sites documentation for more information.
django.contrib.auth.middleware provides three middlewares for use in authentication:
userattribute, representing the currently-logged-in user, to every incoming
*.RemoteUserMiddleware.Middleware for utilizing Web server provided authentication.
*.SessionAuthenticationMiddleware.Allows a user’s sessions to be invalidated when their password changes. This middleware must appear after
For more on user authentication in Django,see Chapter 11.
CSRF Protection Middleware
Adds protection against Cross Site Request Forgeries (CSRF) by adding hidden form fields to POST forms and checking requests for the correct value. See Chapter 19 for more information on CSRF protection.
Simple clickjacking protection via the X-Frame-Options header.
Table 17-1 provides some hints about the ordering of various Django middleware classes:
Table 17-1: Ordering of middleware classes
|UpdateCacheMiddleware||Before those that modify the Vary header (SessionMiddleware, GZipMiddleware, LocaleMiddleware).|
|GZipMiddleware||Before any middleware that may change or use the response body. After UpdateCacheMiddleware: Modifies Vary header.|
|ConditionalGetMiddleware||Before CommonMiddleware: uses its Etag header when USE_ETAGS = True.|
|SessionMiddleware||After UpdateCacheMiddleware: Modifies Vary header.|
|LocaleMiddleware||One of the topmost, after SessionMiddleware (uses session data) and CacheMiddleware (modifies Vary header).|
|CommonMiddleware||Before any middleware that may change the response (it calculates ETags). After GZipMiddleware so it won’t calculate an ETag header on gzipped contents. Close to the top: it redirects when APPEND_SLASH or PREPEND_WWW are set to True.|
|CsrfViewMiddleware||Before any view middleware that assumes that CSRF attacks have been dealt with.|
|AuthenticationMiddleware||After SessionMiddleware: uses session storage.|
|MessageMiddleware||After SessionMiddleware: can use session-based storage.|
|FetchFromCacheMiddleware||After any middleware that modifies the Vary header: that header is used to pick a value for the cache hash-key.|
|FlatpageFallbackMiddleware||Should be near the bottom as it’s a last-resort type of middleware.|
|RedirectFallbackMiddleware||Should be near the bottom as it’s a last-resort type of middleware.|
In the next chapter we will be looking at internationalization in Django.