Setup custom APT sources at build time.

auto/config

@@ -81,3 +81,6 @@ if [ -e config/binary_rootfs/squashfs.sort ]; then
     sort -k2 -n -r config/binary_rootfs/squashfs.sort |
         cut -d' ' -f1 > config/chroot_local-includes/usr/share/amnesia/readahead-list
 fi
+
+# custom APT sources
+tails-custom-apt-sources > config/chroot_sources/tails.chroot

config/chroot_apt/preferences

@@ -213,7 +213,11 @@ Pin-Priority: 999
 Explanation: weirdness in chroot_apt install-binary
 Package: *
 Pin: release o=chroot_local-packages
-Pin-Priority: 1001
+Pin-Priority: 1010
+
+Package: *
+Pin: origin Tails
+Pin-Priority: 1005
 
 Package: *
 Pin: origin mozilla.debian.net

config/chroot_sources/tails.binary

+config/chroot_sources/tails.chroot
\ No newline at end of file