Add binary to convert bazel style credshelper output to the output sdks

accepts

go/cmd/bazelcredswrapper/BUILD.bazel

@@ -0,0 +1,15 @@
+load("@io_bazel_rules_go//go:def.bzl", "go_binary", "go_library")
+
+go_library(
+    name = "bazelcredswrapper_lib",
+    srcs = ["main.go"],
+    importpath = "github.com/bazelbuild/remote-apis-sdks/go/cmd/bazelcredswrapper",
+    visibility = ["//visibility:private"],
+    deps = ["@com_github_golang_glog//:glog"],
+)
+
+go_binary(
+    name = "bazelcredswrapper",
+    embed = [":bazelcredswrapper_lib"],
+    visibility = ["//visibility:public"],
+)

go/cmd/bazelcredswrapper/main.go

@@ -0,0 +1,86 @@
+// Binary bazelcredswrapper is used to authenticate using bazel style credentials helper with the remote-apis-sdks
+
+package main
+
+import (
+	"bytes"
+	"encoding/json"
+	"flag"
+	"fmt"
+	"os"
+	"os/exec"
+	"strings"
+	"time"
+
+	log "github.com/golang/glog"
+)
+
+var (
+	credsPath = flag.String("credentials_helper_path", "", "Path to the user's credentials helper binary.")
+	uri       = flag.String("uri", "", "The URI of the credentials request.")
+)
+
+func main() {
+	defer log.Flush()
+	flag.Parse()
+	log.Flush()
+	var err error
+	if *credsPath == "" {
+		log.Errorf("No credentials helper path provided.")
+		os.Exit(1)
+	}
+	uriObj := fmt.Sprintf(`{"uri":"%v"}`, *uri)
+	cmd := exec.Command(*credsPath, "get")
+	var stdin, stdout, stderr bytes.Buffer
+	cmd.Stdout = &stdout
+	cmd.Stderr = &stderr
+	stdin.Write([]byte(uriObj))
+	cmd.Stdin = &stdin
+	err = cmd.Run()
+	out := stdout.String()
+	if stderr.String() != "" {
+		log.Error(stderr.String())
+	}
+	if err != nil {
+		log.Fatalf("Failed running the credentials helper: %v, with err: %v", *credsPath, err)
+	}
+
+	headers, expiry := parseCredsOut(out)
+	// Bazel-style headers are of the form map[string][]string but we need them
+	// to be of the form map[string]string to match PerRPC credentials
+	hdrs := map[string]string{}
+	for k, v := range headers {
+		hdrs[k] = strings.Join(v, ",")
+	}
+	jsonHdrs, err := json.Marshal(hdrs)
+	if err != nil {
+		log.Error(err)
+		os.Exit(1)
+	}
+	fmt.Printf(`{"headers":%s, "token":"%s", "expiry":"%s"}`, jsonHdrs,
+		"", expiry.Format(time.UnixDate))
+}
+
+type CredshelperOut struct {
+	Headers map[string][]string `json:"headers"`
+	Expires string              `json:"expires"`
+}
+
+func parseCredsOut(out string) (map[string][]string, time.Time) {
+	var credsOut CredshelperOut
+	if err := json.Unmarshal([]byte(out), &credsOut); err != nil {
+		log.Errorf("Error while decoding credshelper output: %v", err)
+		os.Exit(1)
+	}
+	hdrs := credsOut.Headers
+	var exp time.Time
+	if credsOut.Expires != "" {
+		expiry, err := time.Parse(time.RFC3339, credsOut.Expires)
+		if err != nil {
+			log.Errorf("Failed to parse creds expiry: %v", err)
+			os.Exit(1)
+		}
+		exp = expiry
+	}
+	return hdrs, exp
+}