Post build hook signing (#7408)

* docs: Use secret-key-files when demonstrating post-build-hooks

The docs used to recommend calling `nix store sign` in a post-build
hook, but on more recent versions of nix, this results in unsigned
store paths being copied into binary caches. See
https://github.com/NixOS/nix/issues/6960 for details.

Instead, use the `secret-key-files` config option, which signs all
locally-built derivations with the private key.

Co-authored-by: Valentin Gagarin <valentin.gagarin@tweag.io>
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endgame 2022-12-07 22:55:02 +10:00 committed by GitHub
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@ -33,12 +33,17 @@ distribute the public key for verifying the authenticity of the paths.
example-nix-cache-1:1/cKDz3QCCOmwcztD2eV6Coggp6rqc9DGjWv7C0G+rM=
```
Then, add the public key and the cache URL to your `nix.conf`'s
`trusted-public-keys` and `substituters` options:
Then update [`nix.conf`](../command-ref/conf-file.md) on any machine that will access the cache.
Add the cache URL to [`substituters`](../command-ref/conf-file.md#conf-substituters) and the public key to [`trusted-public-keys`](../command-ref/conf-file.md#conf-trusted-public-keys):
substituters = https://cache.nixos.org/ s3://example-nix-cache
trusted-public-keys = cache.nixos.org-1:6NCHdD59X431o0gWypbMrAURkbJ16ZPMQFGspcDShjY= example-nix-cache-1:1/cKDz3QCCOmwcztD2eV6Coggp6rqc9DGjWv7C0G+rM=
Machines that build for the cache must sign derivations using the private key.
On those machines, add the path to the key file to the [`secret-key-files`](../command-ref/conf-file.md#conf-secret-key-files) field in their [`nix.conf`](../command-ref/conf-file.md):
secret-key-files = /etc/nix/key.private
We will restart the Nix daemon in a later step.
# Implementing the build hook
@ -52,14 +57,12 @@ set -eu
set -f # disable globbing
export IFS=' '
echo "Signing paths" $OUT_PATHS
nix store sign --key-file /etc/nix/key.private $OUT_PATHS
echo "Uploading paths" $OUT_PATHS
exec nix copy --to 's3://example-nix-cache' $OUT_PATHS
exec nix copy --to "s3://example-nix-cache" $OUT_PATHS
```
> **Note**
>
>
> The `$OUT_PATHS` variable is a space-separated list of Nix store
> paths. In this case, we expect and want the shell to perform word
> splitting to make each output path its own argument to `nix