Read .netrc in go_repository (#1090)

Fixes #847

internal/go_repository.bzl

@@ -14,10 +14,29 @@
 
 load("@io_bazel_rules_go//go/private:common.bzl", "env_execute", "executable_extension")
 load("@bazel_gazelle//internal:go_repository_cache.bzl", "read_cache_env")
+load("@bazel_tools//tools/build_defs/repo:utils.bzl", "read_netrc", "use_netrc")
 
 # We can't disable timeouts on Bazel, but we can set them to large values.
 _GO_REPOSITORY_TIMEOUT = 86400
 
+# Inspired by @bazel_tools//tools/build_defs/repo:http.bzl
+def _get_auth(ctx, urls):
+    """Given the list of URLs obtain the correct auth dict."""
+    netrcfile = ""
+    if "NETRC" in ctx.os.environ:
+        netrcfile = ctx.os.environ["NETRC"]
+    elif ctx.os.name.startswith("windows"):
+        if "USERPROFILE" in ctx.os.environ:
+            netrcfile = "%s/_netrc" % (ctx.os.environ["USERPROFILE"])
+    elif "HOME" in ctx.os.environ:
+        netrcfile = "%s/.netrc" % (ctx.os.environ["HOME"])
+
+    if netrcfile and ctx.path(netrcfile).exists:
+        netrc = read_netrc(ctx, netrcfile)
+        return use_netrc(netrc, urls, {})
+
+    return {}
+
 def _go_repository_impl(ctx):
     # TODO(#549): vcs repositories are not cached and still need to be fetched.
     # Download the repository or module.
@@ -33,6 +52,7 @@ def _go_repository_impl(ctx):
             sha256 = ctx.attr.sha256,
             stripPrefix = ctx.attr.strip_prefix,
             type = ctx.attr.type,
+            auth = _get_auth(ctx, ctx.attr.urls),
         )
     elif ctx.attr.commit or ctx.attr.tag:
         # repository mode