CAS Server 

CAS Server is a Django application implementing the CAS Protocol 3.0 Specification.

By default, the authentication process uses django internal users but you can easily use any source (see the Authentication backend section and auth classes in the auth.py file)

Features 

Support CAS version 1.0, 2.0, 3.0
Support Single Sign Out
Configuration of services via the Django Admin application
Fine control on which user’s attributes are passed to which service
Possibility to rename/rewrite attributes per service
Possibility to require some attribute values per service
Federated mode between multiple CAS
Supports Django 1.11, 2.2, 3.2, 4.0 and 4.1
Supports Python 3.6+

Dependencies 

django-cas-server depends on the following python packages:

Django >= 1.11 < 4.2
requests >= 2.4
requests_futures >= 0.9.5
lxml >= 3.4

Minimal version of package dependencies are just indicative and means that django-cas-server has been tested with it. Previous versions of dependencies may or may not work.

Additionally, depending on the Authentication backend you plan to use, you may need the following python packages:

ldap3
psycopg2
mysql-python

Here is a table with the name of python packages and the corresponding packages providing them on debian like systems and centos like systems. You should try as much as possible to use system packages as they are automatically updated when you update your system. You can then install Not Available (N/A) packages on your system using pip3 inside a virtualenv as described in the Installation section.

python package	debian like systems	centos like systems
Django	python3-django	python36-django
requests	python3-requests	python36-requests
requests_futures	python3-requests-futures	N/A
lxml	python3-lxml	python36-lxml
ldap3	python3-ldap3	python36-ldap3
psycopg2	python3-psycopg2	python36-psycopg2
mysql-python	python3-mysqldb	python36-mysql

Installation 

The recommended installation mode is to use a virtualenv with --system-site-packages

Make sure that python virtualenv is installed
Install python packages available via the system package manager:

On debian like systems:
```
$ sudo apt-get install python3-django python3-requests python3-lxml python3-requests-futures
```
On debian jessie, you can use the version of python-django available in the backports.

On centos like systems with epel enabled:
```
$ sudo yum install python36-django python36-requests python36-lxml
```

Create a virtualenv:

$ virtualenv -p python3 --system-site-packages cas_venv

And activate it:
```
$ cd cas_venv/; . bin/activate
```

Create a django project:

$ django-admin startproject cas_project
$ cd cas_project

Install django-cas-server. To use the last published release, run:
```
$ pip install django-cas-server
```
Alternatively if you want to use the version of the git repository, you can clone it:
```
$ git clone https://github.com/nitmir/django-cas-server
$ cd django-cas-server
$ pip install -r requirements.txt
```
Then, either run make install to create a python package using the sources of the repository and install it with pip, or place the cas_server directory into your PYTHONPATH (for instance by symlinking cas_server to the root of your django project).
Open cas_project/settings.py in your favourite editor and follow the quick start section.

Quick start 

Add “cas_server” to your INSTALLED_APPS setting like this:

INSTALLED_APPS = (
    'django.contrib.admin',
    ...
    'cas_server',
)

For internationalization support, add “django.middleware.locale.LocaleMiddleware” to your MIDDLEWARE setting like this:

MIDDLEWARE = [
    ...
    'django.middleware.locale.LocaleMiddleware',
    ...
]

Include the cas_server URLconf in your project urls.py like this:

from django.conf.urls import url, include

urlpatterns = [
    url(r'^admin/', admin.site.urls),
    ...
    url(r'^cas/', include('cas_server.urls', namespace="cas_server")),
]

Run python manage.py migrate to create the cas_server models.
You should add some management commands to a crontab: clearsessions, cas_clean_tickets and cas_clean_sessions.
- clearsessions: please see Clearing the session store.
- cas_clean_tickets: old tickets and timed-out tickets do not get purged from the database automatically. They are just marked as invalid. cas_clean_tickets is a clean-up management command for this purpose. It sends SingleLogOut requests to services with timed out tickets and deletes them.
- cas_clean_sessions: Logout and purge users (sending SLO requests) that are inactive more than SESSION_COOKIE_AGE. The default value is 1209600 seconds (2 weeks). You probably should reduce it to something like 86400 seconds (1 day).
You could, for example, do as below:
```
0   0  * * * cas-user /path/to/project/manage.py clearsessions
*/5 *  * * * cas-user /path/to/project/manage.py cas_clean_tickets
5   0  * * * cas-user /path/to/project/manage.py cas_clean_sessions
```
Run python manage.py createsuperuser to create an administrator user.
Start the development server and visit http://127.0.0.1:8000/admin/ to add a first service allowed to authenticate user against the CAS (you’ll need the Admin app enabled). See the Service Patterns section below.
Visit http://127.0.0.1:8000/cas/ to login with your django users.

Settings 

All settings are optional. Add them to settings.py to customize django-cas-server:

Template settings 

CAS_LOGO_URL: URL to the logo shown in the upper left corner on the default template. Set it to False to disable it.
CAS_FAVICON_URL: URL to the favicon (shortcut icon) used by the default templates. Default is a key icon. Set it to False to disable it.
CAS_SHOW_POWERED: Set it to False to hide the powered by footer. The default is True.

CAS_COMPONENT_URLS: URLs to css and javascript external components. It is a dictionary having the five following keys: "bootstrap3_css", "bootstrap3_js", bootstrap4_css, bootstrap4_js, "html5shiv", "respond", "jquery". The default is:

{
    "bootstrap3_css": "//maxcdn.bootstrapcdn.com/bootstrap/3.3.6/css/bootstrap.min.css",
    "bootstrap3_js": "//maxcdn.bootstrapcdn.com/bootstrap/3.3.6/js/bootstrap.min.js",
    "html5shiv": "//oss.maxcdn.com/libs/html5shiv/3.7.0/html5shiv.js",
    "respond": "//oss.maxcdn.com/libs/respond.js/1.4.2/respond.min.js",
    "bootstrap4_css": "//stackpath.bootstrapcdn.com/bootstrap/4.4.1/css/bootstrap.min.css",
    "bootstrap4_js": "//stackpath.bootstrapcdn.com/bootstrap/4.4.1/js/bootstrap.min.js",
    "jquery": "//code.jquery.com/jquery.min.js",
}

if you omit some keys of the dictionary, the default value for these keys is used.

CAS_SHOW_SERVICE_MESSAGES: Messages displayed about the state of the service on the login page. The default is True.
CAS_INFO_MESSAGES: Messages displayed in info-boxes on the html pages of the default templates. It is a dictionary mapping message name to a message dict. A message dict has 3 keys:
- message: A unicode message to display, potentially wrapped around ugettex_lazy
- discardable: A boolean, specify if the users can close the message info-box
- type: One of info, success, warning, danger. The type of the info-box.
CAS_INFO_MESSAGES contains by default one message, cas_explained, which explains roughly the purpose of a CAS. The default is:
```
{
    "cas_explained": {
        "message":_(
            u"The Central Authentication Service grants you access to most of our websites by "
            u"authenticating only once, so you don't need to type your credentials again unless "
            u"your session expires or you logout."
        ),
        "discardable": True,
        "type": "info",  # one of info, success, warning, danger
    },
}
```
CAS_INFO_MESSAGES_ORDER: A list of message names. Order in which info-box messages are displayed. Use an empty list to disable messages display. The default is [].
CAS_LOGIN_TEMPLATE: Path to the template shown on /login when the user is not autenticated. The default is "cas_server/bs4/login.html".
CAS_WARN_TEMPLATE: Path to the template shown on /login?service=... when the user is authenticated and has asked to be warned before being connected to a service. The default is "cas_server/bs4/warn.html".
CAS_LOGGED_TEMPLATE: Path to the template shown on /login when the user is authenticated. The default is "cas_server/bs4/logged.html".
CAS_LOGOUT_TEMPLATE: Path to the template shown on /logout when the user is being disconnected. The default is "cas_server/bs4/logout.html"
CAS_REDIRECT_TO_LOGIN_AFTER_LOGOUT: Should we redirect users to /login after they logged out instead of displaying CAS_LOGOUT_TEMPLATE. The default is False.

Note that the old bootstrap3 template is available in cas_server/bs3/

Authentication settings 

CAS_AUTH_CLASS: A dotted path to a class or a class implementing cas_server.auth.AuthUser. The default is "cas_server.auth.DjangoAuthUser" Available classes bundled with django-cas-server are listed below in the Authentication backend section.
SESSION_COOKIE_AGE: This is a django setting. Here, it controls the delay in seconds after which inactive users are logged out. The default is 1209600 (2 weeks). You probably should reduce it to something like 86400 seconds (1 day).
CAS_TGT_VALIDITY: Max time after which the user MUST reauthenticate. Set it to None for no max time. This can be used to force refreshing cached information only available upon user authentication like the user attributes in federation mode or with the ldap auth in bind mode. The default is None.
CAS_PROXY_CA_CERTIFICATE_PATH: Path to certificate authorities file. Usually on linux the local CAs are in /etc/ssl/certs/ca-certificates.crt. The default is True which tells requests to use its internal certificate authorities. Setting it to False should disable all x509 certificate validation and MUST not be done in production. x509 certificate validation is performed upon PGT issuance.
CAS_SLO_MAX_PARALLEL_REQUESTS: Maximum number of parallel single log out requests sent. If more requests need to be sent, they are queued. The default is 10.
CAS_SLO_TIMEOUT: Timeout for a single SLO request in seconds. The default is 5.
CAS_REMOVE_DJANGO_SESSION_COOKIE_ON_LOGOUT: If True Django session cookie will be removed on logout from CAS server (default False). Note that Django session middleware will generate a new session cookie.
CAS_REMOVE_DJANGO_CSRF_COOKIE_ON_LOGOUT: If True Django csrf cookie will be removed on logout from CAS server (default False). Note that Django csrf middleware will generate a new csrf token cookie.
CAS_REMOVE_DJANGO_LANGUAGE_COOKIE_ON_LOGOUT: If True Django language cookie will be removed on logout from CAS server (default False).

Federation settings 

CAS_FEDERATE: A boolean for activating the federated mode (see the Federation mode section below). The default is False.
CAS_FEDERATE_REMEMBER_TIMEOUT: Time after which the cookie used for “remember my identity provider” expire. The default is 604800, one week. The cookie is called _remember_provider.

New version warnings settings 

CAS_NEW_VERSION_HTML_WARNING: A boolean for diplaying a warning on html pages that a new version of the application is avaible. Once closed by a user, it is not displayed to this user until the next new version. The default is True.
CAS_NEW_VERSION_EMAIL_WARNING: A boolean for sending a email to settings.ADMINS when a new version is available. The default is True.

Tickets validity settings 

CAS_TICKET_VALIDITY: Number of seconds the service tickets and proxy tickets are valid. This is the maximal time between ticket issuance by the CAS and ticket validation by an application. The default is 60.
CAS_PGT_VALIDITY: Number of seconds the proxy granting tickets are valid. The default is 3600 (1 hour).
CAS_TICKET_TIMEOUT: Number of seconds a ticket is kept in the database before sending Single Log Out request and being cleared. The default is 86400 (24 hours).

Tickets miscellaneous settings 

CAS_TICKET_LEN: Default ticket length. All CAS implementations MUST support ST and PT up to 32 chars, PGT and PGTIOU up to 64 chars and it is RECOMMENDED that all tickets up to 256 chars are supported. Here the default is 64.
CAS_LT_LEN: Length of the login tickets. Login tickets are only processed by django-cas-server thus there are no length restrictions on it. The default is CAS_TICKET_LEN.
CAS_ST_LEN: Length of the service tickets. The default is CAS_TICKET_LEN. You may need to lower it to 32 if you use some old clients.
CAS_PT_LEN: Length of the proxy tickets. The default is CAS_TICKET_LEN. This length should be the same as CAS_ST_LEN. You may need to lower it to 32 if you use some old clients.
CAS_PGT_LEN: Length of the proxy granting tickets. The default is CAS_TICKET_LEN.
CAS_PGTIOU_LEN: Length of the proxy granting tickets IOU. The default is CAS_TICKET_LEN.
CAS_LOGIN_TICKET_PREFIX: Prefix of login tickets. The default is "LT".
CAS_SERVICE_TICKET_PREFIX: Prefix of service tickets. The default is "ST". The CAS specification mandates that service tickets MUST begin with the characters ST so you should not change this.
CAS_PROXY_TICKET_PREFIX: Prefix of proxy ticket. The default is "PT".
CAS_PROXY_GRANTING_TICKET_PREFIX: Prefix of proxy granting ticket. The default is "PGT".
CAS_PROXY_GRANTING_TICKET_IOU_PREFIX: Prefix of proxy granting ticket IOU. The default is "PGTIOU".

Mysql backend settings 

Deprecated, see the Sql backend settings. Only useful if you are using the mysql authentication backend:

CAS_SQL_HOST: Host for the SQL server. The default is "localhost".
CAS_SQL_USERNAME: Username for connecting to the SQL server.
CAS_SQL_PASSWORD: Password for connecting to the SQL server.
CAS_SQL_DBNAME: Database name.
CAS_SQL_DBCHARSET: Database charset. The default is "utf8"
CAS_SQL_USER_QUERY: The query performed upon user authentication. The username must be in field username, the password in password, additional fields are used as the user attributes. The default is "SELECT user AS username, pass AS password, users.* FROM users WHERE user = %s"
CAS_SQL_PASSWORD_CHECK: The method used to check the user password. Must be one of the following:
- "crypt" (see <https://en.wikipedia.org/wiki/Crypt_(C)>), the password in the database should begin with $
- "ldap" (see https://tools.ietf.org/id/draft-stroeder-hashed-userpassword-values-01.html) the password in the database must begin with one of {MD5}, {SMD5}, {SHA}, {SSHA}, {SHA256}, {SSHA256}, {SHA384}, {SSHA384}, {SHA512}, {SSHA512}, {CRYPT}.
- "hex_HASH_NAME" with HASH_NAME in md5, sha1, sha224, sha256, sha384, sha512. The hashed password in the database is compared to the hexadecimal digest of the clear password hashed with the corresponding algorithm.
- "plain", the password in the database must be in clear.
The default is "crypt".

Sql backend settings 

Only useful if you are using the sql authentication backend. You must add a "cas_server" database to settings.DATABASES as defined in the django documentation. It is then the database used by the sql backend.

CAS_SQL_USER_QUERY: The query performed upon user authentication. The username must be in field username, the password in password, additional fields are used as the user attributes. The default is "SELECT user AS username, pass AS password, users.* FROM users WHERE user = %s"
CAS_SQL_PASSWORD_CHECK: The method used to check the user password. Must be one of the following:
- "crypt" (see <https://en.wikipedia.org/wiki/Crypt_(C)>), the password in the database should begin with $
- "ldap" (see https://tools.ietf.org/id/draft-stroeder-hashed-userpassword-values-01.html) the password in the database must begin with one of {MD5}, {SMD5}, {SHA}, {SSHA}, {SHA256}, {SSHA256}, {SHA384}, {SSHA384}, {SHA512}, {SSHA512}, {CRYPT}.
- "hex_HASH_NAME" with HASH_NAME in md5, sha1, sha224, sha256, sha384, sha512. The hashed password in the database is compared to the hexadecimal digest of the clear password hashed with the corresponding algorithm.
- "plain", the password in the database must be in clear.
The default is "crypt".
CAS_SQL_PASSWORD_CHARSET: Charset the SQL users passwords was hash with. This is needed to encode the user submitted password before hashing it for comparison. The default is "utf-8".

Ldap backend settings 

Only useful if you are using the ldap authentication backend:

CAS_LDAP_SERVER: Address of the LDAP server. The default is "localhost".
CAS_LDAP_USER: User bind address, for example "cn=admin,dc=crans,dc=org" for connecting to the LDAP server.
CAS_LDAP_PASSWORD: Password for connecting to the LDAP server.
CAS_LDAP_BASE_DN: LDAP search base DN, for example "ou=data,dc=crans,dc=org".
CAS_LDAP_USER_QUERY: Search filter for searching user by username. User entered usernames are escaped using ldap3.utils.conv.escape_bytes. The default is "(uid=%s)"
CAS_LDAP_USERNAME_ATTR: Attribute used for user’s usernames. The default is "uid"
CAS_LDAP_PASSWORD_ATTR: Attribute used for user’s passwords. The default is "userPassword"
CAS_LDAP_PASSWORD_CHECK: The method used to check the user password. Must be one of the following:
- "crypt" (see <https://en.wikipedia.org/wiki/Crypt_(C)>), the password in the database should begin with $
- "ldap" (see https://tools.ietf.org/id/draft-stroeder-hashed-userpassword-values-01.html) the password in the database must begin with one of {MD5}, {SMD5}, {SHA}, {SSHA}, {SHA256}, {SSHA256}, {SHA384}, {SSHA384}, {SHA512}, {SSHA512}, {CRYPT}.
- "hex_HASH_NAME" with HASH_NAME in md5, sha1, sha224, sha256, sha384, sha512. The hashed password in the database is compared to the hexadecimal digest of the clear password hashed with the corresponding algorithm.
- "plain", the password in the database must be in clear.
- "bind", the user credentials are used to bind to the ldap database and retreive the user attribute. In this mode, the settings CAS_LDAP_PASSWORD_ATTR and CAS_LDAP_PASSWORD_CHARSET are ignored, and it is the ldap server that performs the password check.
The default is "ldap".
CAS_LDAP_ATTRS_VIEW: This parameter is only used then CAS_LDAP_PASSWORD_CHECK is set to "bind". If 0 the user attributes are retrieved by connecting to the ldap as CAS_LDAP_USER. If 1 the user attributes are retrieve then the user authenticate using the user credentials and are cached for later use. It means there can be some differences between the attributes in database and the cached ones. See the parameter CAS_TGT_VALIDITY to force user to reauthenticate periodically. The default is 0.
CAS_LDAP_PASSWORD_CHARSET: Charset the LDAP users passwords was hashed with. This is needed to encode the user submitted password before hashing it for comparison. The default is "utf-8".

Test backend settings 

Only useful if you are using the test authentication backend:

CAS_TEST_USER: Username of the test user. The default is "test".
CAS_TEST_PASSWORD: Password of the test user. The default is "test".
CAS_TEST_ATTRIBUTES: Attributes of the test user. The default is {'nom': 'Nymous', 'prenom': 'Ano', 'email': 'anonymous@example.net', 'alias': ['demo1', 'demo2']}.

Authentication backend 

django-cas-server comes with some authentication backends:

dummy backend cas_server.auth.DummyAuthUser: all authentication attempts fail.
test backend cas_server.auth.TestAuthUser: username, password and returned attributes for the user are defined by the CAS_TEST_* settings.
django backend cas_server.auth.DjangoAuthUser: Users are authenticated against django users system. This is the default backend. The returned attributes are the fields available on the user model.
mysql backend cas_server.auth.MysqlAuthUser: Deprecated, use the sql backend instead. see the Mysql backend settings section. The returned attributes are those returned by sql query CAS_SQL_USER_QUERY.
sql backend cas_server.auth.SqlAuthUser: see the Sql backend settings section. The returned attributes are those returned by sql query CAS_SQL_USER_QUERY.
ldap backend cas_server.auth.LdapAuthUser: see the Ldap backend settings section. The returned attributes are those of the ldap node returned by the query filter CAS_LDAP_USER_QUERY.
federated backend cas_server.auth.CASFederateAuth: It is automatically used when CAS_FEDERATE is True. You should not set it manually without setting CAS_FEDERATE to True.

Logs 

django-cas-server logs most of its actions. To enable login, you must set the LOGGING (https://docs.djangoproject.com/en/stable/topics/logging) variable in settings.py.

Users successful actions (login, logout) are logged with the level INFO, failures are logged with the level WARNING and user attributes transmitted to a service are logged with the level DEBUG.

For example to log to syslog you can use :

LOGGING = {
    'version': 1,
    'disable_existing_loggers': False,
    'formatters': {
        'cas_syslog': {
            'format': 'cas: %(levelname)s %(message)s'
        },
    },
    'handlers': {
        'cas_syslog': {
            'level': 'INFO',
            'class': 'logging.handlers.SysLogHandler',
            'address': '/dev/log',
            'formatter': 'cas_syslog',
        },
    },
    'loggers': {
        'cas_server': {
            'handlers': ['cas_syslog'],
            'level': 'INFO',
            'propagate': True,
        },
    },
}

Or to log to a file:

LOGGING = {
    'version': 1,
    'disable_existing_loggers': False,
    'formatters': {
        'cas_file': {
            'format': '%(asctime)s %(levelname)s %(message)s'
        },
    },
    'handlers': {
        'cas_file': {
            'level': 'INFO',
            'class': 'logging.FileHandler',
            'filename': '/tmp/cas_server.log',
            'formatter': 'cas_file',
        },
    },
    'loggers': {
        'cas_server': {
            'handlers': ['cas_file'],
            'level': 'INFO',
            'propagate': True,
        },
    },
}

Service Patterns 

In a CAS context, Service refers to the application the client is trying to access. By extension we use service for the URL of such an application.

By default, django-cas-server does not allow any service to use the CAS to authenticate users. In order to allow services, you need to connect to the django admin interface using a django superuser, and add a first service pattern.

A service pattern comes with 9 fields:

Position: an integer used to change the order in which services are matched against service patterns.
Name: the name of the service pattern. It will be displayed to the users asking for a ticket for a service matching this service pattern on the login page.
Pattern: a regular expression used to match services.
User field: the user attribute to use as username for services matching this service pattern. Leave it empty to use the login name.
Restrict username: if checked, only login names defined below are allowed to get tickets for services matching this service pattern.
Proxy: if checked, allow the creation of Proxy Ticket for services matching this service pattern. Otherwise, only Service Ticket will be created.
Proxy callback: if checked, services matching this service pattern are allowed to retrieve Proxy Granting Ticket. A service with a Proxy Granting Ticket can get Proxy Ticket for other services. Hence you must only check this for trusted services that need it. (For instance, a webmail needs Proxy Ticket to authenticate himself as the user to the imap server).
Single log out: Check it to send Single Log Out requests to authenticated services matching this service pattern. SLO requests are sent to all services the user is authenticated to when the user disconnects.
Single log out callback: The http(s) URL to POST the SLO requests. If empty, the service URL is used. This field is useful to allow non http services (imap, smtp, ftp) to handle SLO requests.

A service pattern has 4 associated models:

Usernames: a list of username associated with the Restrict username field
Replace attribute names: a list of user attributes to send to the service. Choose the name used for sending the attribute by setting Replacement or leave it empty to leave it unchanged.
Replace attribute values: a list of sent user attributes for which value needs to be tweaked. Replace the attribute value by the string obtained by replacing the leftmost non-overlapping occurrences of pattern in string by replace. In replace backslash escapes are processed. Matched groups are captured by 1, 2, etc.
Filter attribute values: a list of user attributes for which value needs to match a regular expression. For instance, service A may need an email address, and you only want user with an email address to connect to it. To do so, put email in Attribute and .* in pattern.

When a user asks for a ticket for a service, the service URL is compared against each service pattern sorted by position. The first service pattern that matches the service URL is chosen. Hence, you should give low position to very specific patterns like ^https://www\.example\.com(/.*)?$ and higher position to generic patterns like ^https://.*. So the service URL https://www.examle.com will use the service pattern for ^https://www\.example\.com(/.*)?$ and not the one for ^https://.*.

Federation mode 

django-cas-server comes with a federation mode. When CAS_FEDERATE is True, users are invited to choose an identity provider on the login page, then, they are redirected to the provider CAS to authenticate. This provider transmits to django-cas-server the user username and attributes. The user is now logged in on django-cas-server and can use services using django-cas-server as CAS.

In federation mode, the user attributes are cached upon user authentication. See the settings CAS_TGT_VALIDITY to force users to reauthenticate periodically and allow django-cas-server to refresh cached attributes.

The list of allowed identity providers is defined using the django admin application. With the development server started, visit http://127.0.0.1:8000/admin/ to add identity providers.

An identity provider comes with 5 fields:

Position: an integer used to tweak the order in which identity providers are displayed on the login page. Identity providers are sorted using position first, then, on equal position, using verbose name and then, on equal verbose name, using suffix.
Suffix: the suffix that will be append to the username returned by the identity provider. It must be unique.
Server url: the URL to the identity provider CAS. For instance, if you are using https://cas.example.org/login to authenticate on the CAS, the server url is https://cas.example.org
CAS protocol version: the version of the CAS protocol to use to contact the identity provider. The default is version 3.
Verbose name: the name used on the login page to display the identity provider.
Display: a boolean controlling the display of the identity provider on the login page. Beware that this do not disable the identity provider, it just hide it on the login page. User will always be able to log in using this provider by fetching /federate/provider_suffix.

In federation mode, django-cas-server build user’s username as follow: provider_returned_username@provider_suffix. Choose the provider returned username for django-cas-server and the provider suffix in order to make sense, as this built username is likely to be displayed to end users in applications.

Then using federate mode, you should add one command to a daily crontab: cas_clean_federate. This command clean the local cache of federated user from old unused users.

You could for example do as below:

10   0  * * * cas-user /path/to/project/manage.py cas_clean_federate