Exercise 1: Set up a kerberos client
====================================

A Kerberos client is easy to set up to work with existing Kerberos
infrastructure.

Setup
-----

Install the Kerberos client packages:

    # apt-get install krb5-user

To show how little configuration is really needed, we will move the
auto-generated config file out of the way (which contains a load of junk
anyway) and create a new minimal one with just 4 lines:

    # mv /etc/krb5.conf /etc/krb5.conf.example
    # editor /etc/krb5.conf

    [libdefaults]
    default_realm = WS.NSRC.ORG
    dns_lookup_realm = true
    dns_lookup_kdc = true

Now check that the ssh client program will try Kerberos authentication. 
It's enabled by default in Ubuntu, but in other operating systems it might
not be.

    # editor /etc/ssh/ssh_config      (on MacOSX it's /etc/ssh_config)

    ...
    GSSAPIAuthentication yes    # check this line present (near end)
    GSSAPIKeyExchange yes       # add this line too
    ...

Testing ssh client
------------------

The class Kerberos setup has an account "testuser" which you can use.

    $ kinit testuser
    ... enter password when prompted
    (password is "nsrc2020" unless you've been told otherwise)

Now you should now be able to login to servers in your Kerberos realm
without re-entering your password:

    $ ssh testuser@noc.ws.nsrg.org
    -- logout, then login somewhere else

    $ ssh testuser@s1.ws.nsrc.org
    -- logout

Have a look at the tickets you've picked up:

    $ klist

You should see your own TGT plus tickets for the servers you've connected
to.

To get rid of them, use `kdestroy`; check that you can no longer login
(the server will give you a password prompt instead)


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Reference material [not part of the exercise]
==================

We've actually enabled two different authentication mechanisms.
`GSSAPIAuthentication` is the standard one (gssapi-with-mic), and just
authenticates the user. `GSSAPIKeyExchange` is a new one (gssapi-keyex)
which also validates the authenticity of the host. It avoids the need
to accept host keys into your `known_hosts` file, because Kerberos already
provides mutual authentication.

`GSSAPIKeyExchange` is available as a patch to ssh, and is included by
default in recent Debian/Ubuntu, RHEL6, and Fedora 13+. But it probably
won't work when connecting to older Unix boxes or to BSD boxes, in
which case you'll fall back to gssapi-with-mic.

More info at http://www.sxw.org.uk/computing/patches/openssh.html

Enabling Kerberos in HTTP clients
---------------------------------

For curl, you must supply an empty username and password in option `-u`

    $ curl --negotiate -u: http://noc.ws.nsrc.org/secure/

For Firefox:

* Go to `about:config`
* Filter on "negotiate"
* `network.negotiate-auth.trusted-uris   ws.nsrc.org`

For Google Chrome: apply the option when starting it up:

    /opt/google/chrome/google-chrome \
      --auth-server-whitelist=*.ws.nsrc.org

Enabling Kerberos in LDAP client
--------------------------------

Under Ubuntu you have to have the appropriate SASL-GSSAPI module installed.

    # apt-get install ldap-utils libsasl2-modules-gssapi-mit

    $ ldapsearch -Y GSSAPI -h ldap.ws.nsrc.org \
        -b "dc=ws,dc=nsrc,dc=org" "(cn=*candler*)"