Single Sign-On¶
This guide will discuss how to set up single sign-on using Microsoft Active Directory.
Note
SSO can only be configured on self-hosted installations.
Conceptual Overview¶
Like every other web application out there, Zammad has its own logic for signing users up, storing their passwords, authenticating them, and managing their sessions.
If your IT department keeps its own user identity store (like Active Directory), Zammad’s SSO support allows you to leverage that existing auth system so that anyone with an account on your local intranet will 1) automatically have an account in Zammad and 2) be able to log in with a single click.
Note
If you don’t have this IT infrastructure but still want one-click login, see Third-Party Authentication for alternatives.
How does it work?¶
Once enabled, single sign-on activates an endpoint
at https://your.zammad.host/auth/sso
.
When the Zammad server receives a GET request at this endpoint
with a valid username in any one of the following:
- an
X-Forwarded-User
request header - a
REMOTE_USER
web server environment variable - an
HTTP_REMOTE_USER
web server environment variable
it creates a new session for that user.
Note
😬 Wait. SSO allows you to sign in with only a username?
In principle, yes.
How is that okay?
In this guide, we configure our web server (Apache)
to intercept all requests to the /auth/sso
endpoint.
Instead of forwarding them to Zammad,
Apache initiates a three-sided login process (Kerberos authentication)
between the itself, the user, and the Active Directory server.
If Active Directory doesn’t recognize the user or their password, Zammad never sees the request, and the session is never created.
What does this all mean?
It means there are many ways you could set up SSO—you don’t need to follow this guide or even use Active Directory or Kerberos—but if you don’t know what you’re doing, you’re going to end up with a massive security hole.
Getting Started¶
Hint
😵 Too busy to handle it on your own?
We’ve got you covered. Our experts offer custom-tailored workshops to get your team up and running fast and with confidence. Just drop us a line!
You will need:
- a Microsoft Active Directory environment with
- root access
- support for AES 256-bit encryption
- a Zammad host with
- root access
- a fully-qualified domain name (FQDN)
- some familiarity with system administration (e.g., Apache configuration)
For best results, set up LDAP integration to make sure your Active Directory and Zammad user accounts are always in sync.
Step 1: Configure Active Directory¶
In the Kerberos authentication scheme, the authentication server (Active Directory) needs to maintain shared secrets with the service (Zammad). To make this possible, we need to register a service principal name (SPN) for Zammad on Active Directory.
Note
These directions have been confirmed on Windows Server 2016.
1a. Create a service account¶
You may use an existing service account if you have one. Admin privileges are not required; a normal user account will do.

Select “This account supports Kerberos AES 256 bit encryption” under Properties > Account > Account options.
1b. Register an SPN for Zammad¶
Note
Replace the following placeholders in the command below:
<zammad-host> : | Zammad FQDN |
---|---|
<service-acct> : | Service account logon name |
<service-acct-pwd> : | |
Service account password | |
<domain> : | Windows domain |
<master-domain-controller> : | |
Master domain controller IP/FQDN |
$ setspn -s HTTP/<zammad-host> <service-acct>
$ ktpass /princ <service-acct>@<domain> \
/mapuser <service-acct> \
/crypto AES256-SHA1 \
/ptype KRB5_NT_PRINCIPAL \
/pass <service-acct-pwd> -SetPass +DumpSalt \
/target <master-domain-controller> \
/out zammad.keytab
1c. Note the secret key and version number¶
The output of the command above contains important data for Step 2e below:
Using legacy password setting method
Failed to set property 'servicePrincipalName' to 'HTTP/<zammad-host>' on Dn 'CN=Zammad Service,DC=<domain>,DC=<tld>': 0x13.
WARNING: Unable to set SPN mapping data.
If <service-acct> already has an SPN mapping installed for HTTP/<zammad-host>, this is no cause for concern.
Building salt with principalname HTTP/<zammad-host> and domain <domain> (encryption type 18)...
Hashing password with salt "<domain><service-acct>".
Key created.
Output keytab to zammad.keytab:
Keytab version: 0x502
keysize 67 <service-acct>@<domain> ptype 1 (KRB5_NT_PRINCIPAL) vno 3 etype 0x12 (AES256-SHA1) keylength 32 (0x5ee827c30c736dd4095c9cbe146eabc216415b1ddb134db6aabd61be8fdf7fb1)
On the last line, take note of:
the secret key: | in parentheses at the end (0x5ee827…) |
---|---|
the secret key version number: | |
preceded by vno (3) |
Step 2: Remove NGINX, Set up Apache + Kerberos¶
Next, the Zammad host must be configured to support Kerberos (and to accept auth credentials provided by the Active Directory server).
In most cases, you would have to recompile NGINX from source with an extra module to enable Kerberos support. To get around this, we will use Apache, which offers Kerberos support through a plug-in module instead.
Note
All commands in this section must be run as root (or with sudo
).
2a. Turn off NGINX¶
$ systemctl stop nginx # turn off nginx
$ systemctl disable nginx # keep it off after reboot
Warning
This will take your Zammad instance offline until Apache is fully configured and running.
If you wish to minimize downtime, you can save this step for last; just bear in mind that Apache will not start if the port it wants to listen on is being used by NGINX.
If for any reason you can’t complete this tutorial, simply turn off Apache and restore NGINX:
$ systemctl stop apache2
$ systemctl disable apache2
$ systemctl enable nginx
$ systemctl start nginx
2b. Install Apache¶
# Ubuntu & Debian
$ apt update
$ apt install apache2 krb5-user libapache2-mod-auth-kerb
# CentOS
$ yum install httpd krb5-workstation mod_auth_kerb
# openSUSE
$ zypper ref
$ zypper install apache2 krb5-client apache2-mod_auth_kerb
2c. Enable Apache modules¶
# Ubuntu, Debian, & openSUSE
$ a2enmod auth_kerb headers rewrite proxy proxy_html proxy_http proxy_wstunnel
On systems without a2enmod
(e.g., CentOS),
add/uncomment the appropriate LoadModule
statements
in your Apache config:
2d. Configure Kerberos¶
Kerberos realm configuration is how you tell the Zammad server how to reach the domain controller (Active Directory server).
Note
Replace the following placeholders in the sample config below:
<domain> : | Windows domain |
---|---|
<domain-controller> : | |
Domain controller IP/FQDN(s) |
|
<master-domain-controller> : | |
Master domain controller IP/FQDN (must not be read-only,
but can be the same as |
2e. Generate keytab¶
Apache needs a Kerberos keytab (key table) to manage its shared secrets with the domain controller.
Note
Replace the following placeholders in the commands below:
<zammad-host> : | Zammad FQDN |
---|---|
<domain> : | Windows domain |
<secret-key> : | Secret key (omit the leading 0x ) |
<vno> : | Secret key version number |
The secret key and version number were found in Step 1: Configure Active Directory above.
$ ktutil
ktutil: addent -key -p HTTP/<zammad-host> -k <vno> -e aes256-cts
Key for HTTP/<zammad-host>@<domain> (hex): <secret-key>
ktutil: list # confirm the entry was added successfully
slot KVNO Principal
---- ---- ---------------------------------------------------------------
1 3 HTTP/<zammad-host>@<domain>
ktutil: wkt /root/zammad.keytab # write keytab to disk
ktutil: quit
Then, place the keytab in the Apache config directory and set the appropriate permissions:
# Ubuntu, Debian, openSUSE
$ mv /root/zammad.keytab /etc/apache2/
$ chown www-data:www-data /etc/apache2/zammad.keytab
$ chmod 400 /etc/apache2/zammad.keytab
# CentOS
$ mv /root/zammad.keytab /etc/httpd/
$ chown apache:apache /etc/httpd/zammad.keytab
$ chmod 400 /etc/httpd/zammad.keytab
2f. Configure Apache¶
Zammad provides a sample virtual host configuration file for Apache.
Add it to your sites-available
directory and enable it:
# Ubuntu, Debian, openSUSE
$ cp /opt/zammad/contrib/apache2/zammad_ssl.conf /etc/apache2/sites-available/
$ chown www-data:www-data /etc/apache2/sites-available/zammad_ssl.conf
$ a2ensite zammad_ssl
# CentOS
$ cp /opt/zammad/contrib/apache2/zammad_ssl.conf /etc/httpd/sites-available/
$ chown apache:apache /etc/httpd/sites-available/zammad_ssl.conf
$ ln -s /etc/httpd/sites-available/zammad_ssl.conf /etc/httpd/sites-enabled/
Also, make sure the following line is present in your Apache configuration:
Now that zammad_ssl.conf
is in place,
it must be modified for your server.
Replace all instances of example.com
with your Zammad FQDN,
and add the following directive to the end of the file
to create your Kerberos SSO endpoint at /auth/sso
:
Note
Replace the following placeholders in the command below:
<zammad-host> : | Zammad FQDN |
---|---|
<domain> : | Windows domain |
The configuration below contains two Krb5KeyTab
lines!
Keep only the one you need.
<LocationMatch "/auth/sso">
SSLRequireSSL
AuthType Kerberos
AuthName "Your Zammad"
KrbMethodNegotiate On
KrbMethodK5Passwd On
KrbAuthRealms <domain>
KrbLocalUserMapping on # strips @REALM suffix from REMOTE_USER variable
KrbServiceName HTTP/<zammad-host>@<domain>
Krb5KeyTab /etc/apache2/zammad.keytab # Ubuntu, Debian, & openSUSE
Krb5KeyTab /etc/httpd/zammad.keytab # CentOS
require valid-user
RewriteEngine On
RewriteCond %{LA-U:REMOTE_USER} (.+)
RewriteRule . - [E=RU:%1,NS]
RequestHeader set X-Forwarded-User "%{RU}e" env=RU
</LocationMatch>
2g. Restart Apache to apply changes¶
$ systemctl restart apache2
Step 3: Enable SSO in Zammad¶
Next, enable “Authencation via SSO” in Zammad’s Admin Panel under Settings > Security > Third-Party Applications:

In Zammad 3.5, this option adds a Sign in using SSO button to the sign-in page.
Note
On older versions of Zammad,
visit https://your.zammad.host/auth/sso
to sign in.
Step 4: Configure Client System (Windows Only)¶
For the full SSO experience (i.e., for passwordless, one-click sign-in), Zammad users must:
- be on the Active Directory server’s local intranet; and
- modify their network settings for the Zammad host to be treated as a local intranet server.

Without this step, users must enter their Active Directory credentials during SSO.
- IE / Edge / Chromium
Tip
This setting can be centrally managed across the entire intranet using a group policy object (GPO).
- Add your Zammad FQDN in Internet Options under Security > Local Intranet > Sites > Advanced.
- Select “Require server verification (https:) for all sites in this zone”.
- Under Security level for this zone > Custom level… > Settings > User Authentication > Logon, select “Automatic logon only in Intranet Zone”.
- Firefox
Note
This option cannot be centrally managed because it is set in the browser rather than Windows Settings.
- Enter
about:config
in the address bar. Click Accept the risk and continue. - Search for the
network.negotiate-auth.trusted-uris
option. - Double-click to edit, then add your Zammad FQDN.
- Restart Firefox to apply your changes.
Enter
about:config
in the address bar to access advanced settings in Firefox.- Enter
Troubleshooting¶
- Are all relevant FQDNs/hostnames reachable from your Active Directory and Zammad servers (including each other’s)?
- Are the system clocks of your Active Directory and Zammad servers synchronized within five minutes of each other? (Kerberos is a time-sensitive protocol.)
Errors in Apache Logs¶
Tip
Try raising your Apache log level temporarily.
Add LogLevel debug
to your virtual host configuration,
then restart the service to apply the changes.
- “an unsupported mechanism was requested”
Does your Active Directory service account have Kerberos AES 256-bit encryption enabled?
If for some reason your server does not support AES 256-bit encryption, the LDAP Wiki has more information about Kerberos encryption types.
- “failed to verify krb5 credentials: Key version is not available”
Did you use the exact version number (
vno
) provided byktpass
when generating your keytab?Try generating it again, just to be sure.
- “unspecified GSS failure. Minor code may provide more information (, No key table entry found for HTTP/FQDN@DOMAIN)”
Does the service name you provided to
setspn
exactly match the one you used when generating your keytab?Try generating it again, just to be sure.
- “No key table entry found for HTTP/FQDN@DOMAIN”
Does your virtual host configuration’s
KrbServiceName
setting exactly match the service name you provided tosetspn
?This setting is case-sensitive.
- “Warning: received token seems to be NTLM, which isn’t supported by the Kerberos module. Check your IE configuration”
- Is your Zammad host accessible at an FQDN? This error may indicate that you configured your Zammad host as a numeric IP address instead.
- “Cannot decrypt ticket for HTTP/FQDN@DOMAIN”
Did you make sure to change the password on your Active Directory service account after enabling 256-bit AES encryption?
And did you make sure to register the SPN (with
ktpass
) and generate your keytab (withktutil
) after changing your password?