fetchgit: add support for netrc file through impure NIX_GIT_SSL_CAINFO env

pkgs/build-support/fetchgit/default.nix

@@ -21,6 +21,11 @@ in
   postFetch ? ""
 , preferLocalBuild ? true
 , fetchLFS ? false
+, # Shell code to build a netrc file for BASIC auth
+  netrcPhase ? null
+, # Impure env vars (https://nixos.org/nix/manual/#sec-advanced-attributes)
+  # needed for netrcPhase
+  netrcImpureEnvVars ? []
 }:
 
 /* NOTE:
@@ -64,10 +69,17 @@ stdenvNoCC.mkDerivation {
 
   inherit url rev leaveDotGit fetchLFS fetchSubmodules deepClone branchName postFetch;
 
+  postHook = if netrcPhase == null then null else ''
+    ${netrcPhase}
+    # required that git uses the netrc file
+    mv {,.}netrc
+    export HOME=$PWD
+  '';
+
   GIT_SSL_CAINFO = "${cacert}/etc/ssl/certs/ca-bundle.crt";
 
-  impureEnvVars = lib.fetchers.proxyImpureEnvVars ++ [
-    "GIT_PROXY_COMMAND" "SOCKS_SERVER"
+  impureEnvVars = lib.fetchers.proxyImpureEnvVars ++ netrcImpureEnvVars ++ [
+    "GIT_PROXY_COMMAND" "NIX_GIT_SSL_CAINFO" "SOCKS_SERVER"
   ];
 
   inherit preferLocalBuild;

pkgs/build-support/fetchgit/nix-prefetch-git

@@ -17,6 +17,10 @@ branchName=$NIX_PREFETCH_GIT_BRANCH_NAME
 out=${out:-}
 http_proxy=${http_proxy:-}
 
+# allow overwritting cacert's ca-bundle.crt with a custom one
+# this can be done by setting NIX_GIT_SSL_CAINFO and NIX_SSL_CERT_FILE enviroment variables for the nix-daemon
+GIT_SSL_CAINFO=${NIX_GIT_SSL_CAINFO:-$GIT_SSL_CAINFO}
+
 # populated by clone_user_rev()
 fullRev=
 humanReadableRev=