gh: support gh as git credential manager for github.com

Co-authored-by: Sumner Evans <me@sumnerevans.com>

modules/programs/gh.nix

@@ -90,6 +90,11 @@ in {
         };
       '';
     };
+
+    enableGitCredentialHelper =
+      mkEnableOption "the gh git credential helper for github.com" // {
+        default = true;
+      };
   };
 
   config = mkIf cfg.enable {
@@ -97,5 +102,9 @@ in {
 
     xdg.configFile."gh/config.yml".source =
       yamlFormat.generate "gh-config.yml" cfg.settings;
+
+    programs.git.extraConfig.credential."https://github.com".helper =
+      mkIf cfg.enableGitCredentialHelper
+      "${cfg.package}/bin/gh auth git-credential";
   };
 }

tests/modules/programs/gh/credential-helper.git.conf

@@ -0,0 +1,2 @@
+[credential "https://github.com"]
+	helper = "@gh@/bin/gh auth git-credential"

tests/modules/programs/gh/credential-helper.nix

@@ -0,0 +1,21 @@
+{ config, lib, pkgs, ... }:
+
+{
+  programs.gh = {
+    enable = true;
+    enableGitCredentialHelper = true;
+  };
+
+  programs.git.enable = true;
+
+  test.stubs = {
+    gh = { };
+    git = { };
+  };
+
+  nmt.script = ''
+    assertFileExists home-files/.config/git/config
+    assertFileContent home-files/.config/git/config \
+      ${./credential-helper.git.conf}
+  '';
+}

tests/modules/programs/gh/default.nix

@@ -1,4 +1,5 @@
 {
   gh-config-file = ./config-file.nix;
+  gh-credential-helper = ./credential-helper.nix;
   gh-warnings = ./warnings.nix;
 }