GSSAPI and Kerberos bindings for Haskell

This library provides a simplified kerberos and GSSAPI bindings for the SPNEGO authentication.

• Modelled after spnego-http-auth-nginx-module
• See this on how to configure browsers
• See this on how to configure keys on the windows AD

Short story

On the AD side, you need to

• Create a new user, whose name should be the service name you'll be using Kerberos authentication on. E.g. app.example.
• Set the "User cannot change password" and "Password never expires" options on the account
• Set a strong password on it

From a Windows cmd.exe window, generate the service principals and keytabs for this user. You need an SPN named host/foo.example.com, and another named HTTP/foo.example.com. It is crucial that foo.example.com is the DNS name of your web site in the intranet, and it is an A record. Given that app.example is the account name you created, you would execute:

C:\> ktpass -princ host/foo.example.com@EXAMPLE.COM -mapuser
EXAMPLECOM\app.example -pass * -out host.keytab -ptype KRB5_NT_PRINCIPAL -crypto All

C:\> ktpass -princ HTTP/foo.example.com@EXAMPLE.COM -mapuser
EXAMPLECOM\app.example -pass * -out http.keytab -ptype KRB5_NT_PRINCIPAL -crypto All

Verify that the correct SPNs are created:

C:\> setspn -Q */foo.example.com

it should yield both the HTTP/ and host/ SPNs, both mapped to the app.example user.

On the server side you need to

Create a krb5.keytab using ktutil, concatenating together the two SPNs keytabs:

# ktutil
ktutil:  rkt host.keytab
ktutil:  rkt http.keytab
ktutil:  wkt /etc/krb5.keytab
ktutil:  quit

Verify that the created keytab file has been built correctly:

# klist -kt /etc/krb5.keytab
Keytab name: WRFILE:/etc/krb5.keytab
KVNO Timestamp         Principal
---- ----------------- --------------------------------------------------------
9 02/19/13 04:02:48 HTTP/foo.example.com@EXAMPLE.COM
8 02/19/13 04:02:48 host/foo.example.com@EXAMPLE.COM

Key version numbers (KVNO) will be different in your case.

Verify that you are able to authenticate using the keytab, without password:

# kinit -5 -V -k -t /etc/krb5.keytab HTTP/foo.example.com
  Authenticated to Kerberos v5

# klist
Ticket cache: FILE:/tmp/krb5cc_0
Default principal: HTTP/foo.example.com@EXAMPLE.COM

Valid starting     Expires            Service principal
02/19/13 17:37:42  02/20/13 03:37:40  krbtgt/EXAMPLE.COM@EXAMPLE.COM
        renew until 02/20/13 17:37:42

Make the keytab file accessible only by appropriate users or groups

# chmod 440 /etc/krb5.keytab
# chown root:nginx /etc/krb5.keytab

There are some issues regarding kvno changes

You can generate keys on the server by

$ kinit ....
# Note down kvno from next commands
$ kvno HTTP/machine.domain.org@DOMAIN.ORG
$ kvno host/machine.domain.org@DOMAIN.ORG
# Add new keys to /etc/krb5.keytab (enter -k KVNO from previous commands)
# Use the ciphers you need for your systems
$ ktutil
addent -password -p HTTP/machine.domain.org@DOMAIN.ORG -k 12 -e arcfour-hmac
addent -password -p host/machine.domain.org@DOMAIN.ORG -k 12 -e arcfour-hmac
wkt /etc/krb5.keytab