add github_access_token option

I'm starting to see rate limit issues with GitHub Actions more
frequently so I propose to make this option more readily available.

README.md

@@ -55,8 +55,7 @@ jobs:
     - uses: actions/checkout@v3
     - uses: cachix/install-nix-action@v18
       with:
-        extra_nix_config: |
-          access-tokens = github.com=${{ secrets.GITHUB_TOKEN }}
+        github_access_token: ${{ secrets.GITHUB_TOKEN }}
     - run: nix build
     - run: nix flake check
 ```
@@ -65,8 +64,12 @@ To install Nix from any commit, go to [the corresponding installer_test action](
 
 ## Inputs (specify using `with:`)
 
+- `github_access_token`: configure nix to pull from github using the given github token. This helps work around rate limit issues.
+
 - `install_url`: specify URL to install Nix from (useful for testing non-stable releases or pinning Nix for example https://releases.nixos.org/nix/nix-2.3.7/install)
 
+- `install_options`: Additional installer flags passed to the installer script.
+
 - `nix_path`: set `NIX_PATH` environment variable, for example `nixpkgs=channel:nixos-unstable`
 
 - `extra_nix_config`: append to `/etc/nix/nix.conf`

action.yml

@@ -9,7 +9,9 @@ inputs:
   nix_path:
     description: 'Set NIX_PATH environment variable.'
   extra_nix_config:
-    description: 'gets appended to `/etc/nix/nix.conf` if passed.'
+    description: 'Gets appended to `/etc/nix/nix.conf` if passed.'
+  github_access_token:
+    description: 'Configure nix to pull from github using the given github token.'
 branding:
   color: 'blue'
   icon: 'sun'
@@ -19,6 +21,7 @@ runs:
     - run : ${{ github.action_path }}/install-nix.sh
       shell: bash
       env:
+        INPUT_GITHUB_ACCESS_TOKEN: ${{ inputs.github_access_token }}
         INPUT_INSTALL_URL: ${{ inputs.install_url }}
         INPUT_INSTALL_OPTIONS: ${{ inputs.install_options }}
         INPUT_NIX_PATH: ${{ inputs.nix_path }}

install-nix.sh

@@ -21,6 +21,10 @@ add_config() {
 add_config "max-jobs = auto"
 # Allow binary caches for user
 add_config "trusted-users = root $USER"
+# Add github access token
+if [[ $INPUT_GITHUB_ACCESS_TOKEN != "" ]]; then
+  add_config "access-tokens" "github.com=$INPUT_GITHUB_ACCESS_TOKEN"
+fi
 # Append extra nix configuration if provided
 if [[ $INPUT_EXTRA_NIX_CONFIG != "" ]]; then
   add_config "$INPUT_EXTRA_NIX_CONFIG"