|
Included on this page:
This guide helps site administrators run a Pubcookie
login server. Everything from setup and configuration to integration
and customization is covered below.
Application server administrators should refer to the
Pubcookie Apache module guide
or ISAPI filter guide for instructions on
deploying a Pubcookie application server which authenticates using your
local login server.
Significant improvements and changes to the login server components
included in Pubcookie 3.3.4:
- Added support for 4096-bit private keys to login cgi.
- Modified login cgi to log user's IP address on Redirect log line.
Significant improvements and changes to the login server components
included in Pubcookie 3.3.2d:
Significant improvements and changes to the login server components
included in Pubcookie 3.3.2c:
- Fixed strlcpy.c bug. Pubcookie's implementation of strlcpy.c had
a null termination bug when the source string (length - 1) exactly fits
the destination string buffer.
- Fixed Javascript call in login cgi when posting data back to the
application server. Added '()' to document.query.submit.
Significant improvements and changes to the login server components
included in Pubcookie 3.3.2:
- Added LDAPS support to LDAP verifier. Enable it with new ldap_tls config file
variable. Configure TLS authentication with new ldap_key_file, ldap_cert_file, and
ldap_ca_file
variables.
- Fixed a bug to avoid a possible loop condition with unexpired
PBC_CLEAR_COOKIE cookies.
Significant improvements and changes to the login server components included in
Pubcookie 3.3.1:
- New default login CGI templates with
more standard XHTML, CSS, and utf-8 encoding.
- Added clear_username_at_logout
site policy to login cgi to control whether the username is cleared
on logout.
- Modified session reauthentication messaging. The login cgi now includes in the granting
message whether or not it handled a reauthentication request.
- Fixed null pointer usage in LDAP verifier when version is empty.
- Modified login cgi to use more consistent audit logging strings.
Prepended the "first kiss" timestamp to authentication success and
failure log file messages.
- Modified login cgi to allow 'http:' and 'https:' in app server uri
query strings without percent encoding the colon.
Significant improvements and changes to the login server components included in
Pubcookie 3.3.0a:
- Applied security fixes to address vulnerabilities described in March 6, 2006
security advisory.
- Fixed problems found in 3.3.0 release with "getcred" flavor's
Kerberos ticket passing.
Significant improvements and changes to the login server components included in
Pubcookie 3.3.0:
- Added AES encryption support. The login cgi will encrypt authentication
messages with the encryption algorithm specified in the authentication request.
- Changed login cgi to use AES encryption on its private login cookies.
- Added PUBCOOKIE_LOGIN_CONFIG_FILE environment variable for defining
an alternate config file for the login cgi.
- Added support for the Apache module's wildcard subdomain key encryption mode
for large multi-user web-hosting environments.
- Added kerberos5_extralife
config file variable to extend the lifetime of delegated tickets past the SSO
lifetime.
- Added lowercase_username
and uppercase_username site
policies to the login cgi for modifying the case of the username.
- Modified minimum LDAP_VENDOR_VERSION in configure script for
better compatibility with Sun LDAP SDK.
- Better handling of stray, malicious, and other spurious cookies.
The login cgi will read all available login cookies to find a valid one.
Previously, it only checked the first one, which might be invalid.
- Other minor login cgi fixes to error handling and cookie clearing.
See doc/CHANGES.txt for bug fixes and other improvements.
In general, the login server components can be upgraded (built and
installed) on a live system while safely maintaining your existing
configuration file (PREFIX/config) and login templates
(PREFIX/login_templates).
Running make install on such a system will do the
following:
- install new keyserver, keyclient, and login cgi binaries into
PREFIX/keyserver, PREFIX/keyclient, and
PREFIX/login/index.cgi, respectively.
- install a set of (possibly updated) generic login templates is
installed into PREFIX/login_templates.default but not
into PREFIX/login_templates if it already exists.
- install a new sample configuration file
(PREFIX/config.login.sample).
Sites should compare their current config file and current templates
against the new ones and resolve significant differences before copying
the new login cgi and other binaries in production locations.
Here are some additional compatibility notes for upgrading between specific
versions:
- Upgrading to 3.3.4:
- User's IP address added to Redirect log line:
Sites that parse the login cgi's log file data should be aware that
the user's IP address has been added to support additional business
purposes (e.g. usage metrics, forensics, troubleshooting). Any scripts
or programs that depend on the format of this data should be tested
for compatibility prior to deploying the new version.
- Upgrading to 3.3:
- AES encryption impact on SSO: Sites upgrading to 3.3 should
be aware that in version 3.3 the login cgi uses AES encryption on all
login cookies, while earlier versions have used DES encryption. As a
result, login cookies obtained by users prior to upgrading the login cgi
will be invalid after the upgrade. This will affect some users' SSO
experience in the following ways: first, after the upgrade some users
will have to reauthenticate where they might not have had to before;
others might notice that the login page no longer remembers (i.e. no
longer pre-fills) their username. Again, this is only around the time of
the upgrade and only for browsing sessions that were started before the
upgrade occurs.
- Upgrading from version 3.2 to 3.3:
- Template changes: The only template changes between versions
3.2 and 3.3 are those from the February 2006 login server security patch
release. Therefore, sites upgrading an unpatched 3.2 login server
(3.2.1a or earlier) to a patched 3.3 login server (3.3.0a or higher)
should update their templates accordingly. Namely, explicit
Content-Type definitions have been added to the following templates:
error, login, nonpost_redirect,
notok, status, pinit_response1, and
logout_part1. Also, the entire HTML comment containing an
unnecessary %url% variable substitution was removed from the
nonpost_redirect template. These files can all be found in
PREFIX/login_templates.default.
Sites upgrading to 3.3 from the patched 3.2.1b release or from a
manually patched 3.2 version should already have these template changes
as they are part of the patch.
- Upgrading from version 3.0/3.1 to 3.3:
- Template changes: Sites upgrading from 3.0/3.1 to version 3.3
must update their templates to account for changes that were introduced
in versions 3.2 and carried into 3.3, as well as for those from the
February 2006 login server security patch release. As noted above, the
patch release updated to the following templates:
error, login, nonpost_redirect,
notok, status, pinit_response1, and
logout_part1. These changes are on top of those from version
3.2, which introduced new variable substitutions in several templates.
Sites should identify these substitutions by comparing these templates
relative to their own production templates:
- login (adds new %reason% and %version% variables)
- form_expired (adds new %time variable)
- logout_part2 (adds new %version% variable)
- pinit_response2 (adds new %version% variable)
The following templates are new (in version 3.2, and therefore in
3.3) and should be reviewed and added to your production templates:
- notok,
notok_badagent,
notok_form_multipart,
notok_generic,
notok_need_ssl
Finally, the following templates have been removed (in version 3.2,
and therefore in 3.3) and therefore can be removed from your production
template directory after upgrading:
- Compatibility note on version 3.1 relays:
- Third-party relays deprecated: The need for the cgi-based
relays introduced in version 3.1 to authenticate across DNS domains was
redressed by the POST-based messaging method introduced in version 3.2
and, thenceforth, use of third-party 3.1 relays has been deprecated. To
continue to support third-party relays at all, you must use the
--enable-unsafe-relay configure option while building the login
cgi. Preferably, upgrade all your application servers using third-party
relays to version 3.2 or higher, and configure them to use the
POST-based messaging method. Then there will be no need to support
third-party relays in your login cgi.
The Pubcookie login server really consists of two separate components
with separate purposes:
- login server cgi
-
The Pubcookie login server uses a CGI program to handle browser
requests. This CGI program, hereafter referred to as the login cgi
or index.cgi, is compiled from C and is a site's central Pubcookie
component. End-users rely on it to authenticate; application servers rely on
it for authentication assertions. The login cgi is typically powered by
Apache HTTP Server software.
- keyserver
-
The Pubcookie login server uses the keyserver component to generate
and distribute symmetric encryption keys for participating servers,
including your Pubcookie login server and all application servers.
The keyserver runs as a service under inetd or xinetd.
The login cgi supports an abstraction called a login flavor. A login
flavor encapsulates a specific set of functionality and features that influence
how and when end-user authentication takes place.
The distribution comes with one login flavor called the basic login
flavor. This login flavor has a rich feature set, including
single sign-on (SSO) user authentication, a pluggable backend authentication
service interface, kiosk mode, and much more.
This guide might, in fact, be described as a guide to the basic login
flavor, it is so tailored to its installation and use.
What the login cgi calls a login flavor, the application
server components call an authentication type. The naming is
rooted in Apache's AuthType directive and it's somewhat
regrettable since they aren't quite the same thing.
For now it's probably enough to say that, unless you build another
login flavor, most application servers will be configured with a single
choice of Pubcookie authentication types, one corresponding directly with
the basic login flavor.
How primary authentication takes place (that is, how usernames
and passwords are actually authenticated) depends on how
the basic login flavor verifies credentials with your backend
authentication service.
The basic login flavor performs username-and-password credential
verification through a simple pluggable interface to backend
authentication services. These plug-ins are called verifiers
and the distribution comes with several:
- kerberos_v5
- verifies credentials using a Kerberos 5 KDC
- ldap
- verifies credentials using an LDAP server
- shadow
- verifies credentials using /etc/shadow
- fork
- verifies credentials using custom forked program
- alwaystrue
- verifies all credentials as successful. good for testing.
Compile-time decisions and run-time configuration determines
which verifier is used by basic login flavor.
These login cgi abstractions help applications to remain independent
of the method, or methods, used by the login server to authenticate user
credentials.
For example, a site might migrate from LDAP-based authentication to Kerberos
authentication. It's attractive to hide the transition from applications.
Here applications would continue to use their institutional "netid"
authentication type, corresponding with their site's basic login flavor,
while the login server administrators transition, transparently, from
one verifier to another.
Other sites may want to be able to choose from different backend
authentication services. For example, the University of Washington uses
the basic login flavor along side and a more secure flavor that uses
SecurID in addition to username and password for primary authentication.
Applications choose which flavor they want by configuring the
appropriate authentication type.
The configure script included in the distribution helps you build
and install the login cgi and keyserver according to your platform and
individual preferences.
To build and install a barebones login server for evaluation and testing,
run the following commands:
$ ./configure --enable-login --disable-apache
$ make
$ make install
This builds the login cgi with support for the basic flavor and the
"alwaystrue" verifier. It also builds the keyserver and keyclient binaries.
Files are installed, and directories created, according to the default
installation directory prefix, henceforth called PREFIX, which
defaults to /usr/local/pubcookie. Use the --prefix
configure option to define an alternative location.
Review the results by listing the installation PREFIX directory
contents.
$ ls
total 240
-rw-r--r-- root root 935 config # config file
-rw-r--r-- root root 935 config.login.sample # sample config
-rwxr-xr-x root root 92229 keyclient* # keyclient
drwxr-xr-x root root 4096 keys/ # keystore
-rwxr-xr-x root root 92929 keyserver* # keyserver
drwxr-xr-x root root 4096 login/ # login cgi dir
drwxr-xr-x root root 4096 login_templates/ # templates
drwxr-xr-x root root 4096 login_templates.default/ # originals
-rw-r--r-- root root 2048 starter.key # starter key
$ ls login
total 204
drwxr-xr-x root root 4096 images/ # images
-rwxr-xr-x root root 99299 index.cgi* # login cgi
Note: initial file permissions assigned by the installation
process may not be acceptable for production use. Please
refer to Appendix B: Permissions & Security
section for a discussion of this subject.
Continue through the setup and configration instructions using
the alwaystrue verifier. After you've gained some familiarity
with a working system, you can rebuild the login cgi to use a
different verifier that goes against your local authentication
service. Review the configure help for the build options.
$ ./configure --help
Refer also to the Kerberos, LDAP, and FastCGI configuration
sections.
SSL key pairs have several functions in the operation of
a Pubcookie login server. One key pair may suffice for all of
them, but two key pairs often works better in practice.
SSL key pair:
The SSL private key and certificate used to SSL-enable Apache can
be reused for the first keypair. This key pair is particularly suited
for use with the keyclient and keyserver because the SSL public key
certificate most likely has been signed and issued by a trusted
Certificate Authority. The login cgi also uses this key pair, but only
for signing and verifying "login" cookies.
Note: the login cgi and keyserver cannot read encrypted RSA private
keys because they can't prompt for the passphrase. To reuse an
encrypted SSL key, you'll first have to remove the passphrase. Refer to Appendix C: OpenSSL Commands for help.
The ssl_key_file and ssl_cert_file config file
variables will point to these keys.
Granting key pair:
A second key pair is used to sign and verify "granting" cookies,
the authentication assertions generated and signed by the login cgi
and verified by application servers. Here the certificate issuer
isn't important, but the SSL public key certificate must be
distributed to other servers. Therefore, a separate "granting" key
pair is often used. Refer to Appendix C: OpenSSL
Commands if you need help generating this key pair.
The granting_cert_file and granting_key_file
config file variables will point to these keys.
Note: the key pairs described in this section (used for SSL and
message signing primarily) are in addition to the symmetric encryption
keys Pubcookie uses for data encryption.
The login cgi and keyserver read configuration settings from a
run-time configuration file. The default location, PREFIX/config,
is compiled in by default.
The login cgi will use an alternate config file if a PUBCOOKIE_LOGIN_CONFIG_FILE
environment variable defines one. This is useful when more than one logical login server
is running on the same machine (using virutal hosts in Apache).
The keyserver will use an alternate config file if the -f <filename>
command-line option defines one.
The config file format is one variable name-value pair per line, except where
a trailing backslash \ character continues a value to the next line.
A sample config file appropriate for a login server is provided (see
PREFIX/config or PREFIX/config.login.sample if you're
upgrading) as a starting point. It will look something like this:
# 1 is a good starting point
logging_level: 1
# the credential verifier used by the basic flavor
basic_verifier: alwaystrue
# SSL session keypair
ssl_key_file: /etc/httpd/conf/ssl.key/server.key
ssl_cert_file: /etc/httpd/conf/ssl.crt/server.crt
# granting keypair
granting_key_file: /usr/local/pubcookie/keys/pubcookie_granting.key
granting_cert_file: /usr/local/pubcookie/keys/pubcookie_granting.cert
# login server config
login_uri: https://login.example.edu/
login_host: login.example.edu
enterprise_domain: .example.edu
logout_prog: /logout/index.cgi
# keyserver config
keymgt_uri: https://login.example.edu:2222
keyserver_client_list: login.example.edu trusted.example.edu
ssl_ca_file: /etc/httpd/conf/ssl.crt/ca-bundle.crt
# site-specific policies
default_l_expire: 8h
Begin editing your config file, using the config
file variable reference as needed for examples and descriptions.
Notes:
-
See how several variables in the example above are derived from the
login server name, login.example.edu. This will be true for your
config file too.
-
The example login server appears to be reusing its SSL key pair
located in server.key and server.crt.
-
The example login server has a separate "granting" key pair. Refer to
Appendix C: OpenSSL Commands if you need help
generating this key pair.
-
The example keyserver appears to be using a file bundle of trusted
Certificate Authorities (i.e., ca-bundle.crt). This file
must contain all the trusted CA root certificates the site is using to
verify keyclient certificates.
Keyserver is designed to run as a service under inetd or xinetd.
If you use inetd, add a line like the following to
/etc/inetd.conf:
2222 stream tcp nowait root /usr/local/pubcookie/keyserver keyserver
If you use xinetd, create /etc/xinetd.d/keyserver with the
following contents:
# description: pubcookie keyserver
service keyserver
{
type = UNLISTED
protocol = tcp
port = 2222
disable = no
socket_type = stream
wait = no
user = root
group = tty
server = /usr/local/pubcookie/keyserver
}
After adding the line to inetd.conf, or the file to xinetd, restart
your inetd or xinetd service.
Note: keyserver requires ssl_key_file and
ssl_cert_file, and either ssl_ca_file or
ssl_ca_path depending on how you handle trusted root CA
certificates. Keyserver also uses granting_cert_file for
distributing your "granting" certificate. And if you want control over
which hosts can request keys, you can do so by defining a
keyserver_client_list for authorizing new hosts.
This section describes how symmetric encryption keys are
managed by the Pubcookie keyserver. It issues keys to all participating
servers, including all login servers and application servers.
The keystore:
A master copy of each 2048-byte host key is stored on
the login server in its keystore, PREFIX/keys, in a filename
based on the server's SSL certificate's Common Name. For example, a site
with a login server and three application servers might have a keystore
like this:
$ ls /usr/local/pubcookie/keys
total 204
-rw-r--r-- root root 2048 weblogin.example.edu
-rw-r--r-- root root 2048 appserver.example.edu
-rw-r--r-- root root 2048 mail.example.edu
-rw-r--r-- root root 2048 my.example.edu
-rw-r--r-- root root 887 pubcookie_granting.key
-rw-r--r-- root root 1224 pubcookie_granting.cert
Each host key can be used for DES encryption or AES encryption. The login
cgi (as of version 3.3) uses AES encryption for login cookies. It uses either
AES or DES for granting cookies, depending on the algorithm specified by the
application server in its authentication request.
New key generation:
New host keys are generated and issued by the keyserver upon request. Running
keyclient on a host initiates the request. If the keyclient host is
authorized, and the keyclient and keyserver trust each other, the
request is fulfilled.
New keyclient host authorization:
If the keyserver_client_list config variable is set, keyserver
performs authorization on all keyclient requests. If it is not set,
keyserver will issue host keys to any trusted keyclient.
When authorization is enabled, grant-or-deny decisions are based on the
presence a host in the keystore. If keyserver finds a host in the
keystore, then that host can request a key. This seems like a catch-22:
to create a new host key in the keystore, the key must already exist
in the keystore. But it's not: site administrators can use
the keyclient's "permit" option to authorize new servers to request host
keys. For example:
$ keyclient -P new.example.edu
Host new.example.edu is permitted
This can be done manually by the login server administrator or by
some kind of automated web-based registration service. The
keyserver_client_list defines which hosts are authorized to use
the permit option, allowing you to authorize new hosts without necessarily
having to log in to the login server to do so.
Trust: SSL/TLS mutual authentication
Pubcookie uses elements of Public-Key Infrastructure (PKI) and SSL/TLS
for mutual server authentication and data privacy between keyclient and
keyserver. Trust is anchored by the Certificate Authorities used to sign,
issue, and verify the certificates exchanged during keyclient connections.
Mutual authentication means the keyclient and keyserver must identify
each other. The keyclient must verify the SSL certificate presented by the
keyserver. Likewise, the keyserver must verify the SSL certificates presented
by keyclients. To do so, they both require trusted CA root certificates to do
the verification. This is configured via ssl_ca_file or
ssl_ca_path, which might point to your own institutional CA root
certificate or pehaps the CA root certificate bundle that comes with
OpenSSL, whatever you happen to be basing your trust policy on.
Working with untrusted keyclients:
An untrusted keyclient is one using a SSL certificate signed by a Certificate
Authority the keyserver doesn't trust. To allow such keyclients to request host
keys without having to obtain another certificate, there's a workaround. The login
server administrator can cache the keyclient's SSL certificate (public key) in
the keystore. The keyserver can then use the public key itself to verify the
keyclient. As a result, an otherwise untrusted keyclient can request host keys
without changing the overall CA trust policy and configuration.
Note: the keyclient's -U cert_file option will upload a certificate
to the keyserver, e.g.:
$ ./keyclient -U untrusted.example.edu.crt
This command can only be run from a trusted host, i.e. in the
keyserver_client_list list.
To generate a symmetric encryption key for your login server, copy
the starter key found in the distribution into your keystore. Use your
login_host name for the filename. For example:
$ cd /usr/local/pubcookie
$ cp starter.key keys/login.example.edu
The starter key allows keyserver to initialize when the keystore
would otherwise be empty. Now you should be able to run keyclient to
request a new host key for the login server based on your current
config file settings:
$ ./keyclient
Set crypt key for login.example.edu
Note: if keyclient is unable to set a new host key, look in syslog for
keyserver error messages.
The login cgi doesn't depend on its own filename or location, so your
primary concern in deploying it should be to create a simple URL that's
easy for users to recognize and trust with their password.
The most common approach is to copy it from
PREFIX/login/index.cgi to your Apache server's root directory,
resulting in a URL such as https://weblogin.example.edu/.
The default HTML templates use relative links to locate the default
stylesheet and inline images. These files are found in a media
subdirectory. Copy the PREFIX/login/media directory to the same
location as the login cgi. It should include one stylesheet file and
three GIF images.
Refer to Appendix A: Apache Configuration
if you're unfamiliar with the directives that control how Apache detects
and handles cgi scripts, particularly as a directory index like
index.cgi.
The login cgi can be opened directly in a browser. This is sometimes
called a pinit (for Pubcookie init, like kinit) since
authentication is requested without being tied to an application. It's a
good way to test your current config file and verifier. Go ahead and
try it now. The login page you see comes from the
PREFIX/login_templates/login and
PREFIX/login_templates/login_pinit templates.
If authentication succeeds, congratulations, you now can deploy an
application server using the Pubcookie Apache module or Pubcookie ISAPI Filter to test the
components together. Then you can go on to build and configure another
verifier that goes against your authentication service and customize the
login cgi templates for your site.
If authentication fails, don't panic, look in your syslog for error
messages from the login cgi and refer to the Logging &
Debugging section for further advice.
The login cgi uses syslog to log all messages. Logging can be
configured using the logging_level
variable. A value of 1 gets you basic audit activity
such as logins and redirects which is most likely sufficient for
normal operation. When additional debugging information is needed
increase the value to 3.
The keyserver also uses syslog and tends to log all critical
error messages. Keyclient uses standard output for its messages.
The login cgi reads HTML templates from the
PREFIX/login_templates directory in order to create login,
logout, error, and redirect pages.
The login cgi will read from an alternative location if the template_root config file
variable is defined.
A set of generic, sample templates is copied into place during
initial installation. A backup set is also copied to
PREFIX/login_templates.default.
Edit these templates (which represent "Example University") to brand
the login server for your organization and to meet local web design
standards.
Refer to the login cgi template
reference for descriptions of each template.
This is all about branding. Some application owners require branding
of the login page with their own login prompt text and icons. The login cgi
support this capability through the use of custom login message templates
(small HTML snippets) configured on the login server. They can't take over
the entire design of the login page, but it does provide a place for
friendlier, custom messages.
A custom login message applies to a single application, so the
corresponding template is stored in a file according to the server name and
application id. The file path is based on the
custom_login_message_dir
configuration variable (the directory containing all the custom login message
templates, which defaults to the same directory as all the other login
templates). The filename is based on the
custom_login_file_prefix
configuration variable (the filename prefix for all custom login message templates)
plus the server name and application id.
For example, to configure a custom login message for an application
on appserver.example.edu with an application id of testapp, you would
place the custom message (HTML snippet) in the following file (based
on default values, of course):
PREFIX/login_templates/custom_login_msg-appserver.example.ed-testapp
You can see where custom login messages are positioned relative to
other elements on the login page by viewing the HTML source of the
login template. They come just before
the reason the user has to authenticate.
The optional PREFIX/ok_browsers file contains a list of
browsers accepted by the login cgi. This file provides a way to block
browsers that either have a known security flaw (i.e., don't forget
cookies when they should) or don't work with Pubcookie. The ok_browsers
file is optional.
The login cgi handles logout requests initiated by, and redirected
from, applications configured with Pubcookie's per-application logout
functionality. Handling these logout requests is built in; no
configuration is necessary to the login cgi itself.
However, through additional configuration you can create a
separate, direct logout URL for your login server (e.g.
https://weblogin.example.edu/logout). You can also tailor the
logout response messages for your favorite applications. Those
are the two subjects of this section.
Note: Pubcookie does not support "global" logout, that is, logout of all
sessions, all cookies, all at once. Rather, it supports per-application-session
logout with optional ability also to logout of the login server. Therefore,
users still must be educated not to leave their browsers open
and unattended without proper precautions such as locking their computer
and using password-protected screensavers. Exiting the browser remains
the best way for users to get logged out of everything at once.
Configuring a Direct Logout URI:
If you want to provide a URL where users can go directly to clear their
single sign-on session (by way of clearning their "login" cookie), it can
be created with the logout_prog config variable and a Unix symbolic
link. Here's an example.
Suppose the login cgi has been installed in the DocumentRoot
directory (e.g. in /var/www/html) with a URL of https://weblogin.example.edu.
To create a logout URI of /logout/ just below that,
i.e., https://weblogin.example.edu/logout/, you'd do
this:
Change to the appropriate directory, create the subdirectory, and make
the symbolic link to your login cgi:
$ cd /var/www/html
$ mkdir logout
$ cd logout
$ ln -s ../index.cgi index.cgi
Adjust the directory according to the location of your login cgi. Now
any request to /logout/ on the server will map to your login
cgi.
Now add the appropriate logout_prog variable to your config file:
logout_prog: /logout/index.cgi
Customizing Logout Responses For Special Apps:
The login cgi builds logout response pages from several templates. One template,
logout_app, which is the most specific to each application, can be overridden
on a per-application basis, as configured and identified by the originating server
name and application id. It requires one app_logout_string config file variable
for each application, where the server name and id are tacked on using dashes. For example:
# custom logout msgs
app_logout_string-appserver.example.edu-testapp: \
<font size="+1">Testapp logout worked just fine.</font>
app_logout_string-webmail.example.edu-webmail: \
<font size="+1">Webmail Logout Successful!</font>
Note: Since the login cgi reads the config file and its HTML
templates on each request, there's no need to recompile the login cgi
in order to modify response messages.
Use the kiosk variable to apply a site policy for reduced
single sign-on duration for identified kiosks. The login cgi supports
matching by user-agent string, remote IP address, or IP address ranges.
For example:
kiosk: 20m Safari/85.6 \
15m Safari \
10m ExampleKiosk 140.142.14.39 140.142.21.* \
1h 140.142.15.10-200
This sets a curiously elaborate, but nonetheless illustrative,
kiosk policy: a 20-minute SSO duration for Safari 85.6, a 15-minute
SSO for all other versions of Safari, a 10-minute SSO to remote browsers
with "ExampleKiosk" in the user-agent string as well as to the remote IP
address 140.142.14.39 and the 140.142.21 subdomain, and a one-hour
SSO duration for IP addresses in the range 140.142.15.10-200.
Matching by user-agent string is particularly useful for
applying reduced SSO to managed kiosks that have a locally
customized user-agent string such as:
User-Agent: Mozilla/4.0 (compatible; MSIE 6.0; ExampleKiosk; Windows NT 5.0)
How to customize user-agent strings is beyond the scope of this guide,
but resources and tools, such as the Internet
Explorer Administration Kit, do exist to help with this task.
This section highlights some of the possible site policies you can
define in your config file. These options may be overlooked, but they
can enhance the user experience and shape the security policy of your
login server.
Use default_l_expire
to define your default single sign-on duration. Primary authentication
occurs when user-provided credentials are verified directly. Subsequent
authentication is based on checking the "login" cookie. This setting
defines how long this cookie is valid. Use form_expire_time
to define how long users have to log in. Taking too long will result in a
new login form (with the form_expired template message included).
The default expiration is 60 seconds. Use static_user_field
to define the editability of the userid field during a single browsing
session. You may want to allow some flexibility or force users to close
the browser before switching between users. - Use the retain_username_on_failed_authn
to define whether the userid is retained after a failed login attempt. Users will
appreciate this if they mistyped their password, not their userid.
Use trim_username_to_atsign
to define whether users can enter a userid that looks like an email address.
Sites that aren't verifying full Kerberos principals (e.g. joe@example.edu) or
userids that look like email addresses can use this feature to provide
some flexibility in this regard, i.e., to trim off the extra realm info
the user added and verify just the proper userid. Use lowercase_username
or uppercase_username to
change the userid to lowercase or uppercase.
Refer to the config file variable
reference to review these variables and the values they take.
To build the login cgi with support for the Kerberos 5 verifier,
run the configure script with the Kerberos option enabled:
./configure --enable-login --disable-apache --enable-krb5
If needed, the configure script has other options for adjusting the
location of the Kerberos header files and libraries.
To configure the login cgi to use the Kerberos verifier, edit your
config file and set basic_verifier to
kerberos_v5. Additionally, two other config
file variables control the Kerberos 5 verifier:
kerberos5_service_name and kerberos5_keytab. For
example:
# kerberos verifier config
basic_verifier: kerberos_v5
kerberos5_service_name: pubcookie
kerberos5_keytab: /usr/local/pubcookie/keys/pubcookie.keytab
Enable the append_realm
variable if you want the Kerberos authentication realm to be appended to
the user name after authentication but before issuing cookies (i.e., target
servers will receive user@REALM.)
Use the default_realm
variable to define a default Kerberos authentication realm to pass to the
verifier when none is submitted via the login form.
To authenticate responses from your Kerberos server, the login server and
Kerberos server must share a service key. You can use an existing service key
or generate a new one with the help of your Kerberos administrator. Keep in
mind that the keytab file that contains your service key must be readable by
the login cgi. Since the login cgi will most likely run as a non-root user,
it's recommended that you use a service key other than the "host" service key
typically stored in /etc/krb5.keytab.
Similar to user keys, service keys have a principal of the form
<service_name>/<hostname>@<realm>. The hostname is
the fully qualified hostname for your login server, and the realm is the
Kerberos realm. But the service name is what counts most to the Kerberos 5
verifier. Your service name can be set with the
kerberos5_service_name variable.
Contact your local Kerberos domain administrator if you need help creating a
service key, generating a keytab file, or otherwise configuring Kerberos
(e.g. /etc/krb5.conf) on your login server.
See doc/krb5-getcred.html for details on how to configure and
use Kerberos credential passing.
To build the login cgi with support for the LDAP verifier,
run the configure script with the LDAP option enabled:
./configure --enable-login --disable-apache --enable-ldap
Note: Other configure options can help you specify the location of
your LDAP header files and libraries. See ./configure
--help.
To configure the login cgi to use the LDAP verifier, set basic_verifier to
ldap in your config file.
To configure the LDAP verifier itself, add an ldap_uri to your config file.
This variable defines how the verifier connects to your LDAP
directory. To enable LDAPS with TLS authentication, configure
ldap_tls,
ldap_key_file,
ldap_cert_file, and
ldap_ca_file.
# ldap verifier config
basic_verifier: ldap
ldap_uri: ldaps://host/o=searchbase???(uid=%s)?x-BindDN=Bind%20DN,x-Password=Password
Note: LDAP in general is not case sensitive, so most implementations
don't enforce case sensitivity on the username (uid) attribute. This may
result in usernames of mixed case being sent to application servers for
the same authenticated user (e.g. jon, Jon, jOn). To prevent this, use the
lowercase_username
site policy to change the username entered to lowercase.
The login cgi and keyserver can be deployed in a redundant
configuration, provided that they share the same cluster
name and settings. Use the
login_servers
variable to configure keyserver to push new host keys to its peers.
The login cgi can run as a FastCGI process. This allows one or
more instances of the login cgi to persist and handle many requests
rather than just one.
FastCGI support is enabled with the --with-fcgi=<path to
fcgi> option. Example Apache configuration follows below; modify
as needed.
LoadModule fastcgi_module libexec/mod_fastcgi.so
FastCgiConfig \
-appConnTimeout 0 \
-idle-Timeout 30 \
-init-start-delay 2 \
-killInterval 300 \
-listen-Queue-Depth 50 \
-maxProcesses 10 \
-maxClassProcesses 2 \
-minProcesses 1 \
-startDelay 10
To support application servers, other system administrators
will need to know the location of your login server, keyserver, and
how trust is handled on your keyserver. That is, which CAs the
keyserver trusts to verify keyclient certificates; and which CA
can be used by the keyclient to verify your keyserver certificate.
The default filename for the login cgi, index.cgi, is a common
name for a cgi program that is executed when a directory's URL is requested.
The DirectoryIndex
directive defines how Apache handles such requests, typically
choosing the first file it finds in its DirectoryIndex list. With
appropriate configuration, this can be your login cgi.
For example, you might use the follow DirectoryIndex directive:
DirectoryIndex index.cgi index.html
Apache also needs to know how to identify cgi scripts by the .cgi
filename extension. Some distributions of Apache have the cgi handler
disabled. Make sure the following line is in your httpd.conf and not
commented out.
AddHandler cgi-script .cgi
Finally, Apache must allow execution of cgi scripts in the directory
where the login cgi is located. If it's outside of a
ScriptAlias
directory, you can control this with the
Options directive.
Options Indexes FollowSymLinks ExecCGI
Due to the important nature of the Pubcookie login server, the only
other services that should be run on the same system are those which
receive an equally high level of scrutiny for security.
Some of the login cgi's supporting files are sensitive, particularly
the two private keys, ssl_key_file and granting_key_file.
In a production environment, non-root users shouldn't be able to read
these files.
However, in a typical Apache configuration the login cgi runs within
a restricted user context defined by the User
and Group
server directives. They are usually set to some non-privileged user and
group (e.g. nobody.nobody).
One approach to permissions is simply to make the sensitive files
owned and readable by the non-privileged Apache user (nobody.nobody
and octal 600, 700 for the keys directory).
drwx------ nobody nobody 4096 keys/
-rw------- nobody nobody 4096 keys/pubcookie_granting.key
-rw------- nobody nobody 4096 keys/pubcookie_session.key
Another approach is to run Apache as a non-privileged user but use a
group that no users are allowed to be in (e.g. nobody.www where
no users are in the www group). Then sensitive files can be
restricted to just root and to the empty group (root.www and
octal 640, 750 for the keys directory). Since the login
cgi runs in the context of the group, it can read the files it needs
to.
drwxr-x--- root www 4096 keys/
-rw-r----- root www 4096 keys/pubcookie_granting.key
-rw-r----- root www 4096 keys/pubcookie_session.key
Note: since the keyserver is run by inetd or xinetd, it is most likely
run as root and therefore can read and write supporting files as needed.
To generate a new RSA private key and self-signed public key certificate,
(for example, for the "granting" key pair), change to the PREFIX/keys
directory and use the following OpenSSL command as an example:
$ cd /usr/local/pubcookie/keys
$ openssl req -new -x509 -out pubcookie_granting.cert \
-newkey rsa:1024 -nodes -keyout pubcookie_granting.key
To remove the pass phrase on an SSL private key:
$ openssl rsa -in server.key -out unencrypted.key
The man pages for x509, rsa, and req
have many other useful OpenSSL command examples.
Significant improvements and changes to the login server components included in
Pubcookie 3.2.1:
- Added kerserver support for subjectAltName wildcards.
- Fixed login cgi to put redirect messages into the normal audit logging stream.
- Added login_host_cookie_domain to make login cookie domain configurable.
- Added remote realm, if present, to authentication success message in flavor_basic logging.
- Fixed LDAP verifier to default to LDAPv3 for all LDAP SDKs and added
"x-Version" parameter to the LDAP URL.
- Revised "fork" verifier to pass username and password via stdin to
the forked executable. The config file variable has been changed from
fork_exe to verify_exe to avoid accidentally
running the wrong executable.
Significant improvements and changes to the login server components included in
Pubcookie 3.2.0:
- Added support for custom per-application login messages
- Added keyserver support to allow keyclient authentication by wildcard
certificates and Subject Alt Names
- Added keyserver support to allow keyclient certificates signed by
untrusted CAs to cache a public key on the keyserver and use it in
server authentication
- Added keyclient -U <certfile> option for admins to upload a
public key certificate to the keyserver
- Added version string to login server template as HTML comment
- Improved POST-based messaging between application servers and login server
- Deprecated the use of third-party relay cgi
|
![[Pubcookie Home Page]](/img/41x35-rings-only.gif){kind=small}
