Django provides full support for anonymous sessions. The session framework\nlets you store and retrieve arbitrary data on a per-site-visitor basis. It\nstores data on the server side and abstracts the sending and receiving of\ncookies. Cookies contain a session ID – not the data itself (unless you’re\nusing the cookie based backend).
\nSessions are implemented via a piece of middleware.
\nTo enable session functionality, do the following:
\nEdit the MIDDLEWARE setting and make sure it contains\n'django.contrib.sessions.middleware.SessionMiddleware'. The default\nsettings.py created by django-admin startproject has\nSessionMiddleware activated.
If you don’t want to use sessions, you might as well remove the\nSessionMiddleware line from MIDDLEWARE and\n'django.contrib.sessions' from your INSTALLED_APPS.\nIt’ll save you a small bit of overhead.
By default, Django stores sessions in your database (using the model\ndjango.contrib.sessions.models.Session). Though this is convenient, in\nsome setups it’s faster to store session data elsewhere, so Django can be\nconfigured to store session data on your filesystem or in your cache.
If you want to use a database-backed session, you need to add\n'django.contrib.sessions' to your INSTALLED_APPS setting.
Once you have configured your installation, run manage.py migrate\nto install the single database table that stores session data.
For better performance, you may want to use a cache-based session backend.
\nTo store session data using Django’s cache system, you’ll first need to make\nsure you’ve configured your cache; see the cache documentation for details.
\n\nIf you have multiple caches defined in CACHES, Django will use the\ndefault cache. To use another cache, set SESSION_CACHE_ALIAS to the\nname of that cache.
Once your cache is configured, you’ve got two choices for how to store data in\nthe cache:
\nSet SESSION_ENGINE to\n"django.contrib.sessions.backends.cache" for a simple caching session\nstore. Session data will be stored directly in your cache. However, session\ndata may not be persistent: cached data can be evicted if the cache fills\nup or if the cache server is restarted.
For persistent, cached data, set SESSION_ENGINE to\n"django.contrib.sessions.backends.cached_db". This uses a\nwrite-through cache – every write to the cache will also be written to\nthe database. Session reads only use the database if the data is not\nalready in the cache.
Both session stores are quite fast, but the simple cache is faster because it\ndisregards persistence. In most cases, the cached_db backend will be fast\nenough, but if you need that last bit of performance, and are willing to let\nsession data be expunged from time to time, the cache backend is for you.
If you use the cached_db session backend, you also need to follow the\nconfiguration instructions for the using database-backed sessions.
To use file-based sessions, set the SESSION_ENGINE setting to\n"django.contrib.sessions.backends.file".
You might also want to set the SESSION_FILE_PATH setting (which\ndefaults to output from tempfile.gettempdir(), most likely /tmp) to\ncontrol where Django stores session files. Be sure to check that your Web\nserver has permissions to read and write to this location.
When SessionMiddleware is activated, each HttpRequest\nobject – the first argument to any Django view function – will have a\nsession attribute, which is a dictionary-like object.
You can read it and write to request.session at any point in your view.\nYou can edit it multiple times.
This is the base class for all session objects. It has the following\nstandard dictionary methods:
\nExample: fav_color = request.session['fav_color']
Example: request.session['fav_color'] = 'blue'
Example: del request.session['fav_color']. This raises KeyError\nif the given key isn’t already in the session.
Example: 'fav_color' in request.session
Example: fav_color = request.session.get('fav_color', 'red')
Example: fav_color = request.session.pop('fav_color', 'blue')
It also has these methods:
\nDeletes the current session data from the session and deletes the session\ncookie. This is used if you want to ensure that the previous session data\ncan’t be accessed again from the user’s browser (for example, the\ndjango.contrib.auth.logout() function calls it).
Sets a test cookie to determine whether the user’s browser supports\ncookies. Due to the way cookies work, you won’t be able to test this\nuntil the user’s next page request. See Setting test cookies below for\nmore information.
\nReturns either True or False, depending on whether the user’s\nbrowser accepted the test cookie. Due to the way cookies work, you’ll\nhave to call set_test_cookie() on a previous, separate page request.\nSee Setting test cookies below for more information.
Deletes the test cookie. Use this to clean up after yourself.
\nSets the expiration time for the session. You can pass a number of\ndifferent values:
\nIf value is an integer, the session will expire after that\nmany seconds of inactivity. For example, calling\nrequest.session.set_expiry(300) would make the session expire\nin 5 minutes.
If value is a datetime or timedelta object, the\nsession will expire at that specific date/time. Note that datetime\nand timedelta values are only serializable if you are using the\nPickleSerializer.
If value is 0, the user’s session cookie will expire\nwhen the user’s Web browser is closed.
If value is None, the session reverts to using the global\nsession expiry policy.
Reading a session is not considered activity for expiration\npurposes. Session expiration is computed from the last time the\nsession was modified.
\nReturns the number of seconds until this session expires. For sessions\nwith no custom expiration (or those set to expire at browser close), this\nwill equal SESSION_COOKIE_AGE.
This function accepts two optional keyword arguments:
\nmodification: last modification of the session, as a\ndatetime object. Defaults to the current time.
expiry: expiry information for the session, as a\ndatetime object, an int (in seconds), or\nNone. Defaults to the value stored in the session by\nset_expiry(), if there is one, or None.
Returns the date this session will expire. For sessions with no custom\nexpiration (or those set to expire at browser close), this will equal the\ndate SESSION_COOKIE_AGE seconds from now.
This function accepts the same keyword arguments as get_expiry_age().
Returns either True or False, depending on whether the user’s\nsession cookie will expire when the user’s Web browser is closed.
Removes expired sessions from the session store. This class method is\ncalled by clearsessions.
Creates a new session key while retaining the current session data.\ndjango.contrib.auth.login() calls this method to mitigate against\nsession fixation.
By default, Django serializes session data using JSON. You can use the\nSESSION_SERIALIZER setting to customize the session serialization\nformat. Even with the caveats described in Write your own serializer, we highly\nrecommend sticking with JSON serialization especially if you are using the\ncookie backend.
For example, here’s an attack scenario if you use pickle to serialize\nsession data. If you’re using the signed cookie session backend and SECRET_KEY is known by an attacker\n(there isn’t an inherent vulnerability in Django that would cause it to leak),\nthe attacker could insert a string into their session which, when unpickled,\nexecutes arbitrary code on the server. The technique for doing so is simple and\neasily available on the internet. Although the cookie session storage signs the\ncookie-stored data to prevent tampering, a SECRET_KEY leak\nimmediately escalates to a remote code execution vulnerability.
A wrapper around the JSON serializer from django.core.signing. Can\nonly serialize basic data types.
In addition, as JSON supports only string keys, note that using non-string\nkeys in request.session won’t work as expected:
>>> # initial assignment\n>>> request.session[0] = 'bar'\n>>> # subsequent requests following serialization & deserialization\n>>> # of session data\n>>> request.session[0] # KeyError\n>>> request.session['0']\n'bar'\nSimilarly, data that can’t be encoded in JSON, such as non-UTF8 bytes like\n'\\xd9' (which raises UnicodeDecodeError), can’t be stored.
See the Write your own serializer section for more details on limitations\nof JSON serialization.
\nSupports arbitrary Python objects, but, as described above, can lead to a\nremote code execution vulnerability if SECRET_KEY becomes known\nby an attacker.
Note that unlike PickleSerializer,\nthe JSONSerializer cannot handle\narbitrary Python data types. As is often the case, there is a trade-off between\nconvenience and security. If you wish to store more advanced data types\nincluding datetime and Decimal in JSON backed sessions, you will need\nto write a custom serializer (or convert such values to a JSON serializable\nobject before storing them in request.session). While serializing these\nvalues is fairly straightforward\n(DjangoJSONEncoder may be helpful),\nwriting a decoder that can reliably get back the same thing that you put in is\nmore fragile. For example, you run the risk of returning a datetime that\nwas actually a string that just happened to be in the same format chosen for\ndatetimes).
Your serializer class must implement two methods,\ndumps(self, obj) and loads(self, data), to serialize and deserialize\nthe dictionary of session data, respectively.
Use normal Python strings as dictionary keys on request.session. This\nis more of a convention than a hard-and-fast rule.
Session dictionary keys that begin with an underscore are reserved for\ninternal use by Django.
Don’t override request.session with a new object, and don’t access or\nset its attributes. Use it like a Python dictionary.
This simplistic view sets a has_commented variable to True after a user\nposts a comment. It doesn’t let a user post a comment more than once:
def post_comment(request, new_comment):\n if request.session.get('has_commented', False):\n return HttpResponse("You've already commented.")\n c = comments.Comment(comment=new_comment)\n c.save()\n request.session['has_commented'] = True\n return HttpResponse('Thanks for your comment!')\nThis simplistic view logs in a “member” of the site:
\ndef login(request):\n m = Member.objects.get(username=request.POST['username'])\n if m.password == request.POST['password']:\n request.session['member_id'] = m.id\n return HttpResponse("You're logged in.")\n else:\n return HttpResponse("Your username and password didn't match.")\n…And this one logs a member out, according to login() above:
def logout(request):\n try:\n del request.session['member_id']\n except KeyError:\n pass\n return HttpResponse("You're logged out.")\nThe standard django.contrib.auth.logout() function actually does a bit\nmore than this to prevent inadvertent data leakage. It calls the\nflush() method of request.session.\nWe are using this example as a demonstration of how to work with session\nobjects, not as a full logout() implementation.
An API is available to manipulate session data outside of a view:
\n>>> from django.contrib.sessions.backends.db import SessionStore\n>>> s = SessionStore()\n>>> # stored as seconds since epoch since datetimes are not serializable in JSON.\n>>> s['last_login'] = 1376587691\n>>> s.create()\n>>> s.session_key\n'2b1189a188b44ad18c35e113ac6ceead'\n>>> s = SessionStore(session_key='2b1189a188b44ad18c35e113ac6ceead')\n>>> s['last_login']\n1376587691\nSessionStore.create() is designed to create a new session (i.e. one not\nloaded from the session store and with session_key=None). save() is\ndesigned to save an existing session (i.e. one loaded from the session store).\nCalling save() on a new session may also work but has a small chance of\ngenerating a session_key that collides with an existing one. create()\ncalls save() and loops until an unused session_key is generated.
If you’re using the django.contrib.sessions.backends.db backend, each\nsession is just a normal Django model. The Session model is defined in\ndjango/contrib/sessions/models.py. Because it’s a normal model, you can\naccess sessions using the normal Django database API:
>>> from django.contrib.sessions.models import Session\n>>> s = Session.objects.get(pk='2b1189a188b44ad18c35e113ac6ceead')\n>>> s.expire_date\ndatetime.datetime(2005, 8, 20, 13, 35, 12)\nNote that you’ll need to call\nget_decoded() to get the session\ndictionary. This is necessary because the dictionary is stored in an encoded\nformat:
>>> s.session_data\n'KGRwMQpTJ19hdXRoX3VzZXJfaWQnCnAyCkkxCnMuMTExY2ZjODI2Yj...'\n>>> s.get_decoded()\n{'user_id': 42}\nBy default, Django only saves to the session database when the session has been\nmodified – that is if any of its dictionary values have been assigned or\ndeleted:
\n# Session is modified.\nrequest.session['foo'] = 'bar'\n\n# Session is modified.\ndel request.session['foo']\n\n# Session is modified.\nrequest.session['foo'] = {}\n\n# Gotcha: Session is NOT modified, because this alters\n# request.session['foo'] instead of request.session.\nrequest.session['foo']['bar'] = 'baz'\nIn the last case of the above example, we can tell the session object\nexplicitly that it has been modified by setting the modified attribute on\nthe session object:
request.session.modified = True\nTo change this default behavior, set the SESSION_SAVE_EVERY_REQUEST\nsetting to True. When set to True, Django will save the session to the\ndatabase on every single request.
Note that the session cookie is only sent when a session has been created or\nmodified. If SESSION_SAVE_EVERY_REQUEST is True, the session\ncookie will be sent on every request.
Similarly, the expires part of a session cookie is updated each time the\nsession cookie is sent.
The session is not saved if the response’s status code is 500.
\nYou can control whether the session framework uses browser-length sessions vs.\npersistent sessions with the SESSION_EXPIRE_AT_BROWSER_CLOSE\nsetting.
By default, SESSION_EXPIRE_AT_BROWSER_CLOSE is set to False,\nwhich means session cookies will be stored in users’ browsers for as long as\nSESSION_COOKIE_AGE. Use this if you don’t want people to have to\nlog in every time they open a browser.
If SESSION_EXPIRE_AT_BROWSER_CLOSE is set to True, Django will\nuse browser-length cookies – cookies that expire as soon as the user closes\ntheir browser. Use this if you want people to have to log in every time they\nopen a browser.
This setting is a global default and can be overwritten at a per-session level\nby explicitly calling the set_expiry() method\nof request.session as described above in using sessions in views.
As users create new sessions on your website, session data can accumulate in\nyour session store. If you’re using the database backend, the\ndjango_session database table will grow. If you’re using the file backend,\nyour temporary directory will contain an increasing number of files.
To understand this problem, consider what happens with the database backend.\nWhen a user logs in, Django adds a row to the django_session database\ntable. Django updates this row each time the session data changes. If the user\nlogs out manually, Django deletes the row. But if the user does not log out,\nthe row never gets deleted. A similar process happens with the file backend.
Django does not provide automatic purging of expired sessions. Therefore,\nit’s your job to purge expired sessions on a regular basis. Django provides a\nclean-up management command for this purpose: clearsessions. It’s\nrecommended to call this command on a regular basis, for example as a daily\ncron job.
Note that the cache backend isn’t vulnerable to this problem, because caches\nautomatically delete stale data. Neither is the cookie backend, because the\nsession data is stored by the users’ browsers.
\nA few Django settings give you control over session\nbehavior:
\n\nSubdomains within a site are able to set cookies on the client for the whole\ndomain. This makes session fixation possible if cookies are permitted from\nsubdomains not controlled by trusted users.
\nFor example, an attacker could log into good.example.com and get a valid\nsession for their account. If the attacker has control over bad.example.com,\nthey can use it to send their session key to you since a subdomain is permitted\nto set cookies on *.example.com. When you visit good.example.com,\nyou’ll be logged in as the attacker and might inadvertently enter your\nsensitive personal data (e.g. credit card info) into the attackers account.
Another possible attack would be if good.example.com sets its\nSESSION_COOKIE_DOMAIN to "example.com" which would cause\nsession cookies from that site to be sent to bad.example.com.
The session dictionary accepts any json serializable value when using\nJSONSerializer or any\npicklable Python object when using\nPickleSerializer. See the\npickle module for more information.
Session data is stored in a database table named django_session .
Django only sends a cookie if it needs to. If you don’t set any session\ndata, it won’t send a session cookie.
SessionStore objectLink to this heading#When working with sessions internally, Django uses a session store object from\nthe corresponding session engine. By convention, the session store object class\nis named SessionStore and is located in the module designated by\nSESSION_ENGINE.
All SessionStore classes available in Django inherit from\nSessionBase and implement data manipulation methods,\nnamely:
exists()
create()
save()
delete()
load()
In order to build a custom session engine or to customize an existing one, you\nmay create a new class inheriting from SessionBase or\nany other existing SessionStore class.
Extending most of the session engines is quite straightforward, but doing so\nwith database-backed session engines generally requires some extra effort (see\nthe next section for details).
\nCreating a custom database-backed session engine built upon those included in\nDjango (namely db and cached_db) may be done by inheriting\nAbstractBaseSession and either SessionStore class.
AbstractBaseSession and BaseSessionManager are importable from\ndjango.contrib.sessions.base_session so that they can be imported without\nincluding django.contrib.sessions in INSTALLED_APPS.
The abstract base session model.
\nPrimary key. The field itself may contain up to 40 characters. The\ncurrent implementation generates a 32-character string (a random\nsequence of digits and lowercase ASCII letters).
\nA string containing an encoded and serialized session dictionary.
\nA datetime designating when the session expires.
\nExpired sessions are not available to a user, however, they may still\nbe stored in the database until the clearsessions management\ncommand is run.
Returns a session store class to be used with this session model.
\nReturns decoded session data.
\nDecoding is performed by the session store class.
\nYou can also customize the model manager by subclassing\nBaseSessionManager:
Returns the given session dictionary serialized and encoded as a string.
\nEncoding is performed by the session store class tied to a model class.
\nSaves session data for a provided session key, or deletes the session\nin case the data is empty.
\nCustomization of SessionStore classes is achieved by overriding methods\nand properties described below:
Implements database-backed session store.
\nOverride this method to return a custom session model if you need one.
\nReturns a new instance of the session model object, which represents\nthe current session state.
\nOverriding this method provides the ability to modify session model\ndata before it’s saved to database.
\nImplements cached database-backed session store.
\nA prefix added to a session key to build a cache key string.
\nThe example below shows a custom database-backed session engine that includes\nan additional database column to store an account ID (thus providing an option\nto query the database for all active sessions for an account):
\nfrom django.contrib.sessions.backends.db import SessionStore as DBStore\nfrom django.contrib.sessions.base_session import AbstractBaseSession\nfrom django.db import models\n\nclass CustomSession(AbstractBaseSession):\n account_id = models.IntegerField(null=True, db_index=True)\n\n @classmethod\n def get_session_store_class(cls):\n return SessionStore\n\nclass SessionStore(DBStore):\n @classmethod\n def get_model_class(cls):\n return CustomSession\n\n def create_model_instance(self, data):\n obj = super().create_model_instance(data)\n try:\n account_id = int(data.get('_auth_user_id'))\n except (ValueError, TypeError):\n account_id = None\n obj.account_id = account_id\n return obj\nIf you are migrating from the Django’s built-in cached_db session store to\na custom one based on cached_db, you should override the cache key prefix\nin order to prevent a namespace clash:
class SessionStore(CachedDBStore):\n cache_key_prefix = 'mysessions.custom_cached_db_backend'\n\n # ...\nThe Django sessions framework is entirely, and solely, cookie-based. It does\nnot fall back to putting session IDs in URLs as a last resort, as PHP does.\nThis is an intentional design decision. Not only does that behavior make URLs\nugly, it makes your site vulnerable to session-ID theft via the “Referer”\nheader.
\n