nongnu: installation-os-nonfree: Set default channels.

* nongnu/system/install.scm (%signing-key,%channels): New variables.
(installation-os-nonfree)[services]: Configure them.
Authorise Nonguix substitute server.

Tested-by: Jonathan Brielmaier <jonathan.brielmaier@web.de>
Signed-off-by: Jonathan Brielmaier <jonathan.brielmaier@web.de>

nongnu/system/install.scm

@@ -2,20 +2,46 @@
 ;;; Copyright © 2019 Alex Griffin <a@ajgrf.com>
 ;;; Copyright © 2019 Pierre Neidhardt <mail@ambrevar.xyz>
 ;;; Copyright © 2022 Jonathan Brielmaier <jonathan.brielmaier@web.de>
+;;; Copyright © 2024 Hilton Chain <hako@ultrarare.space>
 
 ;; Generate a bootable image (e.g. for USB sticks, etc.) with:
-;; $ guix system disk-image nongnu/system/install.scm
+;; $ guix system image --image-type=iso9660 nongnu/system/install.scm
 
 (define-module (nongnu system install)
+  #:use-module (guix channels)
+  #:use-module (guix gexp)
   #:use-module (gnu packages curl)
+  #:use-module (gnu packages package-management)
   #:use-module (gnu packages version-control)
   #:use-module (gnu packages vim)
   #:use-module (gnu packages zile)
+  #:use-module (gnu services)
+  #:use-module (gnu services base)
   #:use-module (gnu system)
   #:use-module (gnu system install)
   #:use-module (nongnu packages linux)
   #:export (installation-os-nonfree))
 
+;; https://substitutes.nonguix.org/signing-key.pub
+(define %signing-key
+  (plain-file "nonguix.pub" "\
+(public-key
+ (ecc
+  (curve Ed25519)
+  (q #C1FD53E5D4CE971933EC50C9F307AE2171A2D3B52C804642A7A35F84F3A4EA98#)))"))
+
+(define %channels
+  (cons* (channel
+          (name 'nonguix)
+          (url "https://gitlab.com/nonguix/nonguix")
+          ;; Enable signature verification:
+          (introduction
+           (make-channel-introduction
+            "897c1a470da759236cc11798f4e0a5f7d4d59fbc"
+            (openpgp-fingerprint
+             "2A39 3FFF 68F4 EF7A 3D29  12AF 6F51 20A0 22FB B2D5"))))
+         %default-channels))
+
 (define installation-os-nonfree
   (operating-system
     (inherit installation-os)
@@ -27,6 +53,19 @@
               git
               neovim
               zile)
-        (operating-system-packages installation-os)))))
+        (operating-system-packages installation-os)))
+    (services
+     (modify-services (operating-system-user-services installation-os)
+       (guix-service-type
+        config => (guix-configuration
+                   (inherit config)
+                   (guix (guix-for-channels %channels))
+                   (authorized-keys
+                    (cons* %signing-key
+                           %default-authorized-guix-keys))
+                   (substitute-urls
+                    `(,@%default-substitute-urls
+                      "https://substitutes.nonguix.org"))
+                   (channels %channels)))))))
 
 installation-os-nonfree