cmd/auth/netrcauth: add a reference GOAUTH implementation using .netrc files

Updates golang/go#26232

Change-Id: Ic6e0003be518e37927a25552b23da4f62eb1072d
Reviewed-on: https://go-review.googlesource.com/c/tools/+/161668
Run-TryBot: Bryan C. Mills <bcmills@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Jay Conrod <jayconrod@google.com>

cmd/auth/netrcauth/netrcauth.go

@@ -0,0 +1,123 @@
+// Copyright 2018 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// netrcauth uses a .netrc file (or _netrc file on Windows) to implement the
+// GOAUTH protocol described in https://golang.org/issue/26232.
+// It expects the location of the file as the first command-line argument.
+//
+// Example GOAUTH usage:
+// 	export GOAUTH="netrcauth $HOME/.netrc"
+//
+// See https://www.gnu.org/software/inetutils/manual/html_node/The-_002enetrc-file.html
+// or run 'man 5 netrc' for a description of the .netrc file format.
+package main
+
+import (
+	"fmt"
+	"io/ioutil"
+	"log"
+	"net/http"
+	"net/url"
+	"os"
+	"strings"
+)
+
+func main() {
+	if len(os.Args) < 2 {
+		fmt.Fprintf(os.Stderr, "usage: %s NETRCFILE [URL]", os.Args[0])
+		os.Exit(2)
+	}
+
+	log.SetPrefix("netrcauth: ")
+
+	if len(os.Args) != 2 {
+		// An explicit URL was passed on the command line, but netrcauth does not
+		// have any URL-specific output: it dumps the entire .netrc file at the
+		// first call.
+		return
+	}
+
+	path := os.Args[1]
+
+	data, err := ioutil.ReadFile(path)
+	if err != nil {
+		if os.IsNotExist(err) {
+			return
+		}
+		log.Fatalf("failed to read %s: %v\n", path, err)
+	}
+
+	u := &url.URL{Scheme: "https"}
+	lines := parseNetrc(string(data))
+	for _, l := range lines {
+		u.Host = l.machine
+		fmt.Printf("%s\n\n", u)
+
+		req := &http.Request{Header: make(http.Header)}
+		req.SetBasicAuth(l.login, l.password)
+		req.Header.Write(os.Stdout)
+		fmt.Println()
+	}
+}
+
+// The following functions were extracted from src/cmd/go/internal/web2/web.go
+// as of https://golang.org/cl/161698.
+
+type netrcLine struct {
+	machine  string
+	login    string
+	password string
+}
+
+func parseNetrc(data string) []netrcLine {
+	// See https://www.gnu.org/software/inetutils/manual/html_node/The-_002enetrc-file.html
+	// for documentation on the .netrc format.
+	var nrc []netrcLine
+	var l netrcLine
+	inMacro := false
+	for _, line := range strings.Split(data, "\n") {
+		if inMacro {
+			if line == "" {
+				inMacro = false
+			}
+			continue
+		}
+
+		f := strings.Fields(line)
+		i := 0
+		for ; i < len(f)-1; i += 2 {
+			// Reset at each "machine" token.
+			// “The auto-login process searches the .netrc file for a machine token
+			// that matches […]. Once a match is made, the subsequent .netrc tokens
+			// are processed, stopping when the end of file is reached or another
+			// machine or a default token is encountered.”
+			switch f[i] {
+			case "machine":
+				l = netrcLine{machine: f[i+1]}
+			case "default":
+				break
+			case "login":
+				l.login = f[i+1]
+			case "password":
+				l.password = f[i+1]
+			case "macdef":
+				// “A macro is defined with the specified name; its contents begin with
+				// the next .netrc line and continue until a null line (consecutive
+				// new-line characters) is encountered.”
+				inMacro = true
+			}
+			if l.machine != "" && l.login != "" && l.password != "" {
+				nrc = append(nrc, l)
+				l = netrcLine{}
+			}
+		}
+
+		if i < len(f) && f[i] == "default" {
+			// “There can be only one default token, and it must be after all machine tokens.”
+			break
+		}
+	}
+
+	return nrc
+}