;;; GNU Guix --- Functional package management for GNU
;;; Copyright © 2016 John Darrington <jmd@gnu.org>
;;;
;;; This file is part of GNU Guix.
;;;
;;; GNU Guix is free software; you can redistribute it and/or modify it
;;; under the terms of the GNU General Public License as published by
;;; the Free Software Foundation; either version 3 of the License, or (at
;;; your option) any later version.
;;;
;;; GNU Guix is distributed in the hope that it will be useful, but
;;; WITHOUT ANY WARRANTY; without even the implied warranty of
;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
;;; GNU General Public License for more details.
;;;
;;; You should have received a copy of the GNU General Public License
;;; along with GNU Guix.  If not, see <http://www.gnu.org/licenses/>.

(define-module (gnu services kerberos)
  #:use-module (gnu services)
  #:use-module (gnu services configuration)
  #:use-module (gnu system pam)
  #:use-module (guix gexp)
  #:use-module (guix records)
  #:use-module (srfi srfi-1)
  #:use-module (srfi srfi-34)
  #:use-module (srfi srfi-35)
  #:use-module (ice-9 match)
  #:export (pam-krb5-configuration
            pam-krb5-configuration?
            pam-krb5-service-type

            krb5-realm
            krb5-realm?

            krb5-configuration
            krb5-configuration?
            krb5-service-type))

\f

(define (uglify-field-name field-name)
  (let ((str (symbol->string field-name)))
    (string-join (string-split (if (string-suffix? "?" str)
                                   (substring str 0 (1- (string-length str)))
                                   str)
                               #\-)
                 "_")))

(define (serialize-field* field-name val)
  (format #t "~a = ~a\n" (uglify-field-name field-name) val))

(define (serialize-string field-name val)
  (if val
      (serialize-field* field-name val) ""))

;; An end-point is an address such as "192.168.0.1"
;; or an address port pair ("foo.example.com" . 109)
(define (end-point? val)
  (or (string? val)
      (and (pair? val)
           (string? (car val))
           (integer? (cdr val)))))

(define (serialize-end-point field-name val)
  (serialize-field* field-name
                   (if (string? val)
                       ;; The [] are needed in the case of IPv6 addresses
                       (format #f "[~a]" val)
                       (format #f "[~a]:~a" (car val) (cdr val)))))


(define (serialize-space-separated-string-list field-name val)
  (if val
      (serialize-field* field-name (string-join val " "))))

(define (comma-separated-string-list? val)
  (and (list? val)
       (and-map (lambda (x)
                  (and (string? x) (not (string-index x #\,))))
                val)))

(define (serialize-comma-separated-string-list field-name val)
  (serialize-field* field-name (string-join val ",")))

(define (comma-separated-integer-list? val)
  (and (list? val)
       (and-map (lambda (x) (integer? x))
                val)))

(define (serialize-comma-separated-integer-list field-name val)
  (if val
      (serialize-field* field-name
                       (string-drop ; Drop the leading comma
                        (fold
                         (lambda (i prev)
                           (string-append prev "," (number->string i)))
                         "" val) 1))))

(define (file-name? val)
  (and (string? val)
       (string-prefix? "/" val)))

(define (serialize-file-name field-name val)
  (serialize-string field-name val))


(define (serialize-boolean field-name val)
  (serialize-string field-name (if val "true" "false")))

(define (non-negative-integer? val)
  (and (exact-integer? val) (not (negative? val))))

(define (serialize-non-negative-integer field-name val)
  (if val
      (serialize-field* field-name val)))

(define (serialize-integer field-name val)
  (if val
      (serialize-field* field-name val)))

(define (free-form-fields? val)
  (match val
    (() #t)
    ((((? symbol?) . (? string)) . val) (free-form-fields? val))
    (_ #f)))

(define (serialize-free-form-fields field-name val)
  (for-each (match-lambda ((k . v) (serialize-field* k v))) val))

(define (realm-list? val)
  (and (list? val)
       (and-map (lambda (x) (krb5-realm? x)) val)))

(define (serialize-realm-list field-name val)
  (format #t "\n[~a]\n" field-name)
  (for-each (lambda (realm)
              (format #t "\n~a = {\n" (krb5-realm-name realm))
              (for-each (lambda (field)
                          (unless (eq? 'name (configuration-field-name field))
                            ((configuration-field-serializer field)
                             (configuration-field-name field)
                             ((configuration-field-getter field)
                              realm)))) krb5-realm-fields)

              (format #t "}\n")) val))

\f

;; For a more detailed explanation of these fields see man 5 krb5.conf
(define-configuration krb5-realm
  (name
   (string #f)
   "The name of the realm.")

  (kdc
   (end-point #f)
   "The host and port on which the realm's Key Distribution Server listens.")

  (admin-server
   (string #f)
   "The Host running the administration server for the realm.")

  (master-kdc
   (string #f)
   "If an attempt to get credentials fails because of an invalid password, 
the client software will attempt to contact the master KDC.")

  (kpasswd-server
   (string #f)
   "The server where password changes are performed.")

  (auth-to-local
   (free-form-fields '())
   "Rules to map between principals and local users.")

  (auth-to-local-names
   (free-form-fields '())
   "Explicit mappings between principal names and local user names.")

  (http-anchors
   (free-form-fields '())
   "Useful only when http proxy is used to access KDC or KPASSWD.")

  ;; The following are useful only for working with V4 services
  (default-domain
    (string #f)
    "The domain used to expand host names when translating Kerberos 4 service
principals to Kerberos 5 principals")

  (v4-instance-convert
   (free-form-fields '())
   "Exceptions to the default-domain mapping rule.")

  (v4-realm
   (string #f)
   "Used  when the V4 realm name and the V5 realm name are not the same, but
still share the same principal names and passwords"))



;; For a more detailed explanation of these fields see man 5 krb5.conf
(define-configuration krb5-configuration
  (allow-weak-crypto?
   (boolean #f)
   "If true, permits access to services which only offer weak encryption.")

  (ap-req-checksum-type
   (non-negative-integer #f)
   "The type of the AP-REQ checksum.")

  (canonicalize?
   (boolean #f)
   "Should principals in initial ticket requests be canonicalized?")

  (ccache-type
   (non-negative-integer #f)
   "The format of the credential cache type.")

  (clockskew
   (non-negative-integer #f)
   "Maximum allowable clock skew in seconds (default 300).")

  (default-ccache-name
    (file-name #f)
    "The name of the default credential cache.")

  (default-client-keytab-name
    (file-name #f)
    "The name of the default keytab for client credentials.")

  (default-keytab-name
    (file-name #f)
    "The name of the default keytab file.")

  (default-realm
    (string #f)
    "The realm to be accessed if not explicitly specified by clients.")

  (default-tgs-enctypes
    (free-form-fields '())
    "Session key encryption types when making TGS-REQ requests.")

  (default-tkt-enctypes
    (free-form-fields '())
    "Session key encryption types when making AS-REQ requests.")

  (dns-canonicalize-hostname?
   (boolean #t)
   "Whether name lookups will be used to canonicalize host names for use in 
service principal names.")

  (dns-lookup-kdc?
   (boolean #f)
 "Should DNS SRV records should be used to locate the KDCs and other servers 
not appearing in the realm specification")

  (err-fmt
   (string #f)
   "Custom error message formatting. If not #f error messages will be formatted 
by substituting a normal error message for %M and an error code for %C in the 
value.")

  (forwardable?
   (boolean #f)
   "Should initial tickets be forwardable by default?")

  (ignore-acceptor-hostname?
   (boolean #f)
   "When accepting GSSAPI or krb5 security contexts for host-based service 
principals, ignore any hostname passed by the calling application, and allow 
clients to authenticate to any service principal in the keytab matching the 
service name and realm name.")

  (k5login-authoritative?
   (boolean #t)
   "If this flag is true, principals must be listed in a local user's k5login
file to be granted login access, if a ~/.k5login file exists.")

  (k5login-directory
   (string #f)
   "If not #f, the library will look for a local user's @file{k5login} file 
within the named directory (instead of the user's home directory), with a 
file name corresponding to the local user name.")

  (kcm-mach-service
   (string #f)
   "The name of the bootstrap service used to contact the KCM daemon for the 
KCM credential cache type.")

  (kcm-socket
   (file-name #f)
 "Path to the Unix domain socket used to access the KCM daemon for the KCM 
credential cache type.")

  (kdc-default-options
   (non-negative-integer #f)
   "Default KDC options (logored for multiple values) when requesting initial 
tickets.")

  (kdc-timesync
   (non-negative-integer #f)
   "Attempt to compensate for clock skew between the KDC and client.")

  (kdc-req-checksum-type
   (non-negative-integer #f)
   "The type of checksum to use for the KDC requests. Relevant only for DES 
keys")

  (noaddresses?
   (boolean #t)
   "If true, initial ticket requests will not be made with address restrictions.
This enables their use across NATs.")

  (permitted-enctypes
   (space-separated-string-list #f)
   "All encryption types that are permitted for use in session key encryption.")

  (plugin-base-dir
   (file-name #f)
   "The directory where krb5 plugins are located.")

  (preferred-preauth-types
   (comma-separated-integer-list #f)
   "The preferred pre-authentication types which the client will attempt before 
others.")

  (proxiable?
   (boolean #f)
   "Should initial tickets be proxiable by default?")

  (rdns?
   (boolean #t)
   "Should reverse DNS lookup be used in addition to forward name lookup to 
canonicalize host names for use in service principal names.")

  (realm-try-domains
   (integer #f)
   "Should a host's domain components should be used to determine the Kerberos 
realm of the host.")

  (renew-lifetime
   (non-negative-integer #f)
   "The default renewable lifetime for initial ticket requests.")

  (safe-checksum-type
   (non-negative-integer #f)
   "The type of checksum to use for the KRB-SAFE requests.")

  (ticket-lifetime
   (non-negative-integer #f)
   "The default lifetime for initial ticket requests.")

  (udp-preference-limit
   (non-negative-integer #f)
   "When sending messages to the KDC, the library will try using TCP
before UDP if the size of the message greater than this limit.")

  (verify-ap-req-nofail?
   (boolean #f)
 "If true, then attempts to verify initial credentials will fail if the client
machine does not have a keytab.")

  (realms
   (realm-list '())
   "The list of realms which clients may access."))


(define (krb5-configuration-file config)
  "Create a Kerberos 5 configuration file based on CONFIG"
  (mixed-text-file "krb5.conf"
                   "[libdefaults]\n\n"
                   (with-output-to-string
                     (lambda ()
                       (serialize-configuration config
                                                krb5-configuration-fields)))))

(define (krb5-etc-service config)
  (list `("krb5.conf" ,(krb5-configuration-file config))))


(define krb5-service-type
  (service-type (name 'krb5)
                (extensions
                 (list (service-extension etc-service-type
                                          krb5-etc-service)))))


\f

(define-record-type* <pam-krb5-configuration>
  pam-krb5-configuration  make-pam-krb5-configuration
  pam-krb5-configuration?
  (pam-krb5               pam-krb5-configuration-pam-krb5
                          (default pam-krb5))
  (minimum-uid            pam-krb5-configuration-minimum-uid
                          (default 1000)))

(define (pam-krb5-pam-service config)
  "Return a PAM service for Kerberos authentication."
  (lambda (pam)
    (define pam-krb5-module
      #~(string-append #$(pam-krb5-configuration-pam-krb5 config)
                       "/lib/security/pam_krb5.so"))

    (let ((pam-krb5-sufficient
           (pam-entry
            (control "sufficient")
            (module pam-krb5-module)
            (arguments
             (list
              (format #f "minimum_uid=~a"
                      (pam-krb5-configuration-minimum-uid config)))))))
      (pam-service
       (inherit pam)
       (auth (cons* pam-krb5-sufficient
                    (pam-service-auth pam)))
       (session (cons* pam-krb5-sufficient
                       (pam-service-session pam)))
       (account (cons* pam-krb5-sufficient
                       (pam-service-account pam)))))))

(define (pam-krb5-pam-services config)
  (list (pam-krb5-pam-service config)))

(define pam-krb5-service-type
  (service-type (name 'pam-krb5)
                (extensions
                 (list
                  (service-extension pam-root-service-type
                                     pam-krb5-pam-services)))))