3 files changed, 193 insertions, 0 deletions
diff --git a/src/cmd/go/internal/auth/auth.go b/src/cmd/go/internal/auth/auth.go
new file mode 100644
index 0000000..fe5a89d
--- /dev/null
+++ b/src/cmd/go/internal/auth/auth.go
@@ -0,0 +1,25 @@
+// Copyright 2019 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.
+
+// Package auth provides access to user-provided authentication credentials.
+package auth
+
+import "net/http"
+
+// AddCredentials fills in the user's credentials for req, if any.
+// The return value reports whether any matching credentials were found.
+func AddCredentials(req *http.Request) (added bool) {
+	host := req.URL.Hostname()
+
+	// TODO(golang.org/issue/26232): Support arbitrary user-provided credentials.
+	netrcOnce.Do(readNetrc)
+	for _, l := range netrc {
+		if l.machine == host {
+			req.SetBasicAuth(l.login, l.password)
+			return true
+		}
+	}
+
+	return false
+}
diff --git a/src/cmd/go/internal/auth/netrc.go b/src/cmd/go/internal/auth/netrc.go
new file mode 100644
index 0000000..0107f20
--- /dev/null
+++ b/src/cmd/go/internal/auth/netrc.go
@@ -0,0 +1,110 @@
+// Copyright 2019 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.
+
+package auth
+
+import (
+	"os"
+	"path/filepath"
+	"runtime"
+	"strings"
+	"sync"
+)
+
+type netrcLine struct {
+	machine  string
+	login    string
+	password string
+}
+
+var (
+	netrcOnce sync.Once
+	netrc     []netrcLine
+	netrcErr  error
+)
+
+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
+}
+
+func netrcPath() (string, error) {
+	if env := os.Getenv("NETRC"); env != "" {
+		return env, nil
+	}
+	dir, err := os.UserHomeDir()
+	if err != nil {
+		return "", err
+	}
+	base := ".netrc"
+	if runtime.GOOS == "windows" {
+		base = "_netrc"
+	}
+	return filepath.Join(dir, base), nil
+}
+
+func readNetrc() {
+	path, err := netrcPath()
+	if err != nil {
+		netrcErr = err
+		return
+	}
+
+	data, err := os.ReadFile(path)
+	if err != nil {
+		if !os.IsNotExist(err) {
+			netrcErr = err
+		}
+		return
+	}
+
+	netrc = parseNetrc(string(data))
+}
diff --git a/src/cmd/go/internal/auth/netrc_test.go b/src/cmd/go/internal/auth/netrc_test.go
new file mode 100644
index 0000000..e06c545
--- /dev/null
+++ b/src/cmd/go/internal/auth/netrc_test.go
@@ -0,0 +1,58 @@
+// 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.
+
+package auth
+
+import (
+	"reflect"
+	"testing"
+)
+
+var testNetrc = `
+machine incomplete
+password none
+
+machine api.github.com
+  login user
+  password pwd
+
+machine incomlete.host
+  login justlogin
+
+machine test.host
+login user2
+password pwd2
+
+machine oneline login user3 password pwd3
+
+machine ignore.host macdef ignore
+  login nobody
+  password nothing
+
+machine hasmacro.too macdef ignore-next-lines login user4 password pwd4
+  login nobody
+  password nothing
+
+default
+login anonymous
+password gopher@golang.org
+
+machine after.default
+login oops
+password too-late-in-file
+`
+
+func TestParseNetrc(t *testing.T) {
+	lines := parseNetrc(testNetrc)
+	want := []netrcLine{
+		{"api.github.com", "user", "pwd"},
+		{"test.host", "user2", "pwd2"},
+		{"oneline", "user3", "pwd3"},
+		{"hasmacro.too", "user4", "pwd4"},
+	}
+
+	if !reflect.DeepEqual(lines, want) {
+		t.Errorf("parseNetrc:\nhave %q\nwant %q", lines, want)
+	}
+}