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<html> <!-- SECTION: Getting Started --> <head> <title>Using Kerberos Authentication</title> <link rel="stylesheet" type="text/css" href="../cups-printable.css"> </head> <body> <h1 class="title">Using Kerberos Authentication</h1> <p>CUPS allows you to use a Key Distribution Center (KDC) for authentication on your local CUPS server and when printing to a remote authenticated queue. This document describes how to configure CUPS to use Kerberos authentication and provides links to the MIT help pages for configuring Kerberos on your systems and network.</p> <blockquote><b>Note:</b> Kerberos authentication is deprecated starting in CUPS 2.4.0. OAuth 2.0 is the recommended SSO replacement.</blockquote> <h2 class="title" id="REQUIREMENTS">System Requirements</h2> <p>The following are required to use Kerberos with CUPS:</p> <ol> <li>Heimdal Kerberos (any version) or MIT Kerberos (1.6.3 or newer)</li> <li>Properly configured Domain Name System (DNS) infrastructure (for your servers): <ol type="a"> <li>DNS server(s) with static IP addresses for all CUPS servers or configured to allow DHCP updates to the host addresses and</li> <li>All CUPS clients and servers configured to use the same DNS server(s).</li> </ol> </li> <li>Properly configured Kerberos infrastructure: <ol type='a'> <li>KDC configured to allow CUPS servers to obtain Service Granting Tickets (SGTs) for the "host" and "HTTP" services/principals,</li> <li>LDAP-based user accounts - both OpenDirectory and ActiveDirectory provide this with the KDC, and</li> <li>CUPS clients and servers bound to the same KDC and LDAP server(s).</li> </ol> </li> </ol> <h2 class="title" id="KRB5">Configuring Kerberos on Your System</h2> <p>Before you can use Kerberos with CUPS, you will need to configure Kerberos on your system and setup a system as a KDC. Because this configuration is highly system and site-specific, please consult the following on-line resources provided by the creators of Kerberos at the Massachusetts Institute of Technology (MIT):</p> <ul> <li><a href="http://web.mit.edu/kerberos/" target="_blank">Kerberos: The Network Authentication Protocol</a></li> <li><a href="http://web.mit.edu/macdev/KfM/Common/Documentation/faq-osx.html" target="_blank">Kerberos on macOS Frequently Asked Questions</a></li> </ul> <p>The Linux Documentation Project also has a HOWTO on Kerberos:</p> <ul> <li><a href="http://tldp.org/HOWTO/html_single/Kerberos-Infrastructure-HOWTO/" target="_blank">Kerberos Infrastructure HOWTO</a></li> </ul> <h2 class="title" id="CUPS">Configuring CUPS to Use Kerberos</h2> <p>Once you have configured Kerberos on your system(s), you can then enable Kerberos authentication by selecting the <tt>Negotiate</tt> authentication type. The simplest way to do this is using the <tt>cupsctl(8)</tt> command on your server(s):</p> <pre class="command"><kbd>cupsctl DefaultAuthType=Negotiate</kbd></pre> <p>You can also enable Kerberos from the web interface by checking the <VAR>Use Kerberos Authentication</VAR> box and clicking <VAR>Change Settings</VAR>:</p> <pre class="command">https://server.example.com:631/admin</pre> <p>After you have enabled Kerberos authentication, use the built-in "authenticated" policy or your own custom policies with the printers you will be sharing. See <a href="policies.html">Managing Operation Policies</a> for more information.</p> <h2 class="title" id="IMPLEMENT">Implementation Information</h2> <p>CUPS implements Kerberos over HTTP using GSSAPI and the service/principal names "host/server.example.com" for command-line access and "HTTP/server.example.com" for web-based access, where "server.example.com" is replaced by your CUPS server's hostname. Because of limitations in the HTTP GSSAPI protocol extension, only a single domain/KDC is supported for authentication. The (experimental) HTTP extension is described in <a href="http://tools.ietf.org/html/rfc4559">RFC 4559</a>.</p> <p>When doing printing tasks that require authentication, CUPS requests single-use "tickets" from your login session to authenticate who you are. These tickets give CUPS a username of the form "user@REALM", which is then truncated to just "user" for purposes of user and group checks.</p> <p>In order to support printing to a shared printer, CUPS runs the IPP or SMB backend as the owner of the print job so it can obtain the necessary credentials when the job is de-spooled to the server.</p> </body> </html>