kdcproxy 1.0.0

A kerberos KDC HTTP proxy WSGI module.

Welcome to kdcproxy!

This package contains a WSGI module for proxying KDC requests over HTTP by following the [MS-KKDCP] protocol. It aims to be simple to deploy, with minimal configuration.

Deploying kdcproxy

The kdcproxy module follows the standard WSGI protocol for deploying Python web applications. This makes configuration simple. Simply load up your favorite WSGI-enabled web server and point it to the module. For example, if you wish to use mod_wsgi, try something like this:

WSGIDaemonProcess kdcproxy processes=2 threads=15 maximum-requests=1000 \
    display-name=%{GROUP}
WSGIImportScript /usr/lib/python3.6/site-packages/kdcproxy/__init__.py \
    process-group=kdcproxy application-group=kdcproxy
WSGIScriptAlias /KdcProxy /usr/lib/python3.6/site-packages/kdcproxy/__init__.py
WSGIScriptReloading Off

<Location "/KdcProxy">
    Satisfy Any
    Order Deny,Allow
    Allow from all
    WSGIProcessGroup kdcproxy
    WSGIApplicationGroup kdcproxy
</Location>

[MS-KKDCP] suggests /KdcProxy as end point. For more information, see the documentation of your WSGI server.

Configuring kdcproxy

When kdcproxy receives a request, it needs to know where to proxy it to. This is the purpose of configuration: discovering where to send kerberos requests.

One important note: where the underlying configuration does not specify TCP or UDP, both will be attempted. TCP will be attempted before UDP, hence setting udp_preference_limit = 1 is not required for kdcproxy itself (though krb5 may still need it). This permits the use of longer timeouts and prevents possible lockouts when the KDC packets contain OTP token codes (which should preferably be sent to only one server).

Automatic Configuration

By default, no configuration is necessary. In this case, kdcproxy will use REALM DNS SRV record lookups to determine remote KDC locations.

Master Configuration File

If you wish to have more detailed configuration, the first place you can configure kdcproxy is the master configuration file. This file exists at the location specified in the environment variable KDCPROXY_CONFIG. If this variable is unspecified, the default locations are /usr/local/etc/kdcproxy.conf or /etc/kdcproxy.conf. This configuration file takes precedence over all other configuration modules. This file is an ini-style configuration with a special section [global]. Two parameters are available in this section: configs and use_dns.

The use_dns allows you to enable or disable use of DNS SRV record lookups.

The configs parameter allows you to load other configuration modules for finding configuration in other places. The configuration modules specified in here will have priority in the order listed. For instance, if you wished to read configuration from MIT libkrb5, you would set the following:

[global] configs = mit

Aside from the [global] section, you may also specify manual configuration for realms. In this case, each section is the name of the realm and the parameters are kerberos or kpasswd. These specify the locations of the remote servers for krb5 AS requests and kpasswd requests, respectively. For example:

[EXAMPLE.COM] kerberos = kerberos+tcp://kdc.example.com:88 kpasswd = kpasswd+tcp://kpasswd.example.com:464

The realm configuration parameters may list multiple servers separated by a space. The order the realms are specified in will be respected by kdcproxy when forwarding requests. The port number is optional. Possible schemes are:

• kerberos://

• kerberos+tcp://

• kerberos+udp://

• kpasswd://

• kpasswd+tcp://

• kpasswd+udp://

MIT libkrb5

If you load the mit config module in the master configuration file, kdcproxy will also read the config using libkrb5 (usually /etc/krb5.conf). If this module is used, kdcproxy will respect the DNS settings from the [libdefaults] section and the realm configuration from the [realms] section.

For more information, see the documentation for MIT’s krb5.conf.

Configuration reloading

kdcproxy reads its configurtion files when package is imported and a global WSGI application object is instantiated. For now kdcproxy does neither monitor its configuration files for changes nor supports runtime updates. You have to restart the WSGI process to make modification available. With Apache HTTP and mod_wsgi, a reload of the server also restarts all WSGI daemons.

Configuring a client for kdcproxy

HTTPS proxy support is available since Kerberos 5 release 1.13. Some vendors have backported the feature to older versions of krb5, too. In order to use a HTTPS proxy, simply point the kdc and kpasswd options to the proxy URL like explained in [HTTPS proxy] configuration guide. Your /etc/krb5.conf may look like this:

[libdefaults]
    default_realm = EXAMPLE.COM

[realms]
    EXAMPLE.COM = {
        http_anchors = FILE:/etc/krb5/cacert.pem
        kdc = https://kerberos.example.com/KdcProxy
        kpasswd_server = https://kerberos.example.com/KdcProxy
}

To debug the feature, set the environment variable KRB5_TRACE to /dev/stdout. When the feature is correctly configured, you should see two POST requests in the access log of the WSGI server and a line containing Sending HTTPS request in the debug output of kinit:

$ env KRB5_TRACE=/dev/stdout kinit user
[1037] 1431509096.26305: Getting initial credentials for [e-mail]
[1037] 1431509096.26669: Sending request (169 bytes) to EXAMPLE.COM
[1037] 1431509096.26939: Resolving hostname kerberos.example.com
[1037] 1431509096.34377: TLS certificate name matched "kerberos.example.com"
[1037] 1431509096.38791: Sending HTTPS request to https 128.66.0.1:443
[1037] 1431509096.46387: Received answer (344 bytes) from https 128.66.0.1:443
[1037] 1431509096.46411: Terminating TCP connection to https 128.66.0.1:443
...

If kinit still connects to port 88/TCP or port 88/UDP, then System Security Services Daemon’s Kerberos locator plugin might override the settings in /etc/krb5.conf. With the environment variable SSSD_KRB5_LOCATOR_DEBUG=1, kinit and sssd_krb5_locator_plugin print out additional debug information. To disable the KDC locator feature, edit /etc/sssd/sssd.conf and set krb5_use_kdcinfo to False:

[domain/example.com] krb5_use_kdcinfo = False

Don’t forget to restart SSSD!

[MS-KKDCP]: http://msdn.microsoft.com/en-us/library/hh553774.aspx

[HTTPS Proxy]: http://web.mit.edu/kerberos/krb5-current/doc/admin/https.html