Support loading http credentials from netrc

rust/private/repository_utils.bzl

@@ -1,5 +1,11 @@
 """Utility macros for use in rules_rust repository rules"""
 
+load(
+    "@bazel_tools//tools/build_defs/repo:utils.bzl",
+    "read_netrc",
+    "read_user_netrc",
+    "use_netrc",
+)
 load("//rust:known_shas.bzl", "FILE_KEY_TO_SHA")
 load(
     "//rust/platform:triple_mappings.bzl",
@@ -804,10 +810,39 @@ def load_arbitrary_tool(
 
     return {archive_path: sha256}
 
+# The function is copied from the main branch of bazel_tools.
+# It should become available there from version 8.0.0,
+# We should remove this function when we upgrade minimum supported
+# version to 8.0.0.
+# https://github.com/bazelbuild/bazel/blob/d37762b494a4e122d46a5a71e3a8cc77fa15aa25/tools/build_defs/repo/utils.bzl#L424-L446
+def _get_auth(ctx, urls):
+    """Utility function to obtain the correct auth dict for a list of urls from .netrc file.
+
+    Support optional netrc and auth_patterns attributes if available.
+
+    Args:
+      ctx: The repository context of the repository rule calling this utility
+        function.
+      urls: the list of urls to read
+
+    Returns:
+      the auth dict which can be passed to repository_ctx.download
+    """
+    if hasattr(ctx.attr, "netrc") and ctx.attr.netrc:
+        netrc = read_netrc(ctx, ctx.attr.netrc)
+    elif "NETRC" in ctx.os.environ:
+        netrc = read_netrc(ctx, ctx.os.environ["NETRC"])
+    else:
+        netrc = read_user_netrc(ctx)
+    auth_patterns = {}
+    if hasattr(ctx.attr, "auth_patterns") and ctx.attr.auth_patterns:
+        auth_patterns = ctx.attr.auth_patterns
+    return use_netrc(netrc, urls, auth_patterns)
+
 def _make_auth_dict(ctx, urls):
     auth = getattr(ctx.attr, "auth", {})
     if not auth:
-        return {}
+        return _get_auth(ctx, urls)
     ret = {}
     for url in urls:
         ret[url] = auth