## Single Sign On

Cockpit can use Kerberos for Single Sign On authentication, where users are automatically authenticated if they have a valid Kerberos ticket.

## Server Requirements

To authenticate users, the server that Cockpit is running on must be joined to a domain. This can usually be accomplished using the `realm join example.com` command.

The domain must be resolvable by DNS. For instance, the SRV records of the kerberos server should be resolvable:

    $ host -t SRV  _kerberos._udp.example.com
    _kerberos._udp.example.com has SRV record 0 100 88 dc.example.com

The server running Cockpit should have a fully qualified name that ends with the domain name.

There must be a valid Kerberos host key for the server in the `/etc/krb5.keytab` file. Alternatively, if you would like to use a different keytab, you can do so by placing it in `/etc/cockpit/krb5.keytab`. It may be necessary to create a kerberos service principal and update the keytab if it is not present. Depending on your domain type different service names are required:

Active Directory | `HOST/server.example.com@EXAMPLE.COM`
IPA and MIT | `HTTP/server.example.com@EXAMPLE.COM`

When joining an IPA domain with Cockpit and the `ipa` command line tool is available, both the service principal name and a `/etc/cockpit/krb5.keytab` get created automatically, so that Kerberos based single sign on into Cockpit works out of the box. If you want/need to do this by hand or in a script, the corresponding commands with IPA are:

    $ sudo ipa service-add --ok-as-delegate=true --force HTTP/server.example.com@EXAMPLE.COM
    $ sudo ipa-getkeytab -p HTTP/server.example.com@EXAMPLE.COM -k /etc/cockpit/krb5.keytab

The following command can be used to list the `/etc/cockpit/krb5.keytab`:

    $ sudo klist -k /etc/cockpit/krb5.keytab

Lastly accounts from the domain must be resolvable to unix accounts on the server running Cockpit. For example:

    $ getent passwd user@example.com
    user@example.com:*:381001109:381000513:User Name:/home/user:/bin/sh

If you wish to delegate your kerberos credentials to Cockpit, and allow Cockpit to then connect to other machines using those credentials, you should enable delegation for the hosts running Cockpit, and in some cases the `HTTP` service as well. When joining an IPA domain, this is enabled by default.

Domain admins (usually the `admins@example.com` group) should normally also be able to administer any joined machine. Enable sudo access for that group with the following command on the IPA server, for version 4.7.1 and later:

    ipa-advise enable-admins-sudo | sh -ex

On earlier FreeIPA versions, run these commands instead, as a domain admin on any joined machine:

    ipa sudorule-add --hostcat=all --cmdcat=all All
    ipa sudorule-add-user --groups=admins All

Note that this does not change security properties; domain admins can give this privilege to themselves, so it is safe to enable by default.

## Client Requirements

The client side, where your web browser is running, should have a valid kerberos ticket in the current user session. A command like this will get one:

    $ kinit user@EXAMPLE.COM
    Password for user@EXAMPLE.COM:

In addition your browser must be usually be configured to allow kerberos authentication for the domain.

Mozilla Firefox | Go to `about:config` and set the `network.negotiate-auth.trusted-uris` setting to your domain name preceded by a dot, ie: `.example.com`
Google Chrome | On Linux: create the file `/etc/opt/chrome/policies/managed/example-com.json` with the contents:
    {
      "AuthServerWhitelist": "*example.com"
    }
and restart the browser. On other platforms, exit your browser completely, and start it with a command line like this: `google-chrome --auth-server-whitelist=*example.com`

Use a fully qualified server name (with the domain name at the end) to access Cockpit in your web browser.

If you wish to connect from one server to another in Cockpit using kerberos SSO, then you have to explicitly enable all sorts of things. For starters, make sure that delegated credentials are allowed by your domain (see above). Next when requesting your kerberos ticket make sure that forwardable tickets are requested:

    $ kinit -f user@EXAMPLE.COM
    Password for user@EXAMPLE.COM:

Make sure that the forwardable flag `F` is present in your ticket:

    $ klist -f
    Ticket cache: KEYRING:persistent:1000:1000
    Default principal: user@EXAMPLE.COM

    Valid starting       Expires              Service principal
    18.03.2017 05:39:23  19.03.2017 05:39:20  krbtgt/EXAMPLE.COM@EXAMPLE.COM
    	Flags: FIA

Lastly configure your browser to allow delegated, forwardable kerberos credentials to be sent to Cockpit:

Mozilla Firefox | Go to `about:config` and set the `network.negotiate-auth.delegation-uris` setting to your domain name preceded by a dot, ie: `.example.com`
Google Chrome | On Linux: create the file `/etc/opt/chrome/policies/managed/example-com.json` with the contents:
    {
      "AuthServerWhitelist": "*example.com",
      "AuthNegotiateDelegateWhitelist": "*example.com"
    }
and restart the browser. On other platforms, exit your browser completely, and start it with a command line like this: `google-chrome --auth-server-whitelist=*example.com --auth-negotiate-delegate-whitelist=*example.com`