1<HTML> 2<!-- SECTION: Getting Started --> 3<HEAD> 4 <TITLE>Using Kerberos Authentication</TITLE> 5 <LINK REL="STYLESHEET" TYPE="text/css" HREF="../cups-printable.css"> 6</HEAD> 7<BODY> 8 9<H1 CLASS="title">Using Kerberos Authentication</H1> 10 11<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> 12 13 14<H2 CLASS="title"><A NAME="REQUIREMENTS">System Requirements</A></H2> 15 16<p>The following are required to use Kerberos with CUPS:</p> 17 18<ol> 19 20 <li>Heimdal Kerberos (any version) or MIT Kerberos (1.6.3 or newer)</li> 21 22 <li>Properly configured Domain Name System (DNS) infrastructure (for your servers):<ol type='a'> 23 <li>DNS server(s) with static IP addresses for all CUPS servers or configured to allow DHCP updates to the host addresses and</li> 24 <li>All CUPS clients and servers configured to use the same 25DNS server(s).</li> 26 </ol></li> 27 28 <li>Properly configured Kerberos infrastructure:<ol type='a'> 29 <li>KDC configured to allow CUPS servers to obtain Service Granting Tickets (SGTs) for the "host" and "HTTP" services/principals,</li> 30 <li>LDAP-based user accounts - both OpenDirectory and ActiveDirectory provide this with the KDC, and</li> 31 <li>CUPS clients and servers bound to the same KDC and LDAP 32 server(s).</li> 33 </ol></li> 34 35</ol> 36 37 38<H2 CLASS="title"><A NAME="KRB5">Configuring Kerberos on Your System</A></H2> 39 40<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> 41 42<UL> 43 44 <LI><A HREF="http://web.mit.edu/kerberos/">Kerberos: The Network Authentication Protocol</A></LI> 45 46 <LI><A HREF="http://web.mit.edu/macdev/KfM/Common/Documentation/faq-osx.html">Kerberos 47 on macOS Frequently Asked Questions</A></LI> 48 49</UL> 50 51<P>The Linux Documentation Project also has a HOWTO on Kerberos:</P> 52 53<UL> 54 55 <LI><A HREF="http://tldp.org/HOWTO/html_single/Kerberos-Infrastructure-HOWTO/">Kerberos 56 Infrastructure HOWTO</A></LI> 57 58</UL> 59 60 61<H2 CLASS="title"><A NAME="CUPS">Configuring CUPS to Use Kerberos</A></H2> 62 63<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> 64 65<PRE CLASS="command"> 66<KBD>cupsctl DefaultAuthType=Negotiate</KBD> 67</PRE> 68 69<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> 70 71<PRE CLASS="command"> 72http://server.example.com:631/admin 73</PRE> 74 75<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> 76 77 78<H2 CLASS="title"><A NAME="IMPLEMENT">Implementation Information</A></H2> 79 80<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 HTTP extension is described in <a href="http://tools.ietf.org/html/rfc4559">RFC 4559</a>.</P> 81 82<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> 83 84<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> 85 86</BODY> 87</HTML> 88