net/smtp: add CRAM-MD5 authentication

R=golang-dev, edsrzf, bradfitz, rsc
CC=golang-dev
https://golang.org/cl/5451087

diff --git a/src/pkg/net/smtp/auth.go b/src/pkg/net/smtp/auth.go
index 10a757fc64307f1c420145f594e74d0d7dfd8df5..6f0cde0d2833d43a0ebf963b608923d05371e444 100644 (file)
--- a/src/pkg/net/smtp/auth.go
+++ b/src/pkg/net/smtp/auth.go
@@ -4,7 +4,11 @@
 
 package smtp
 
-import "errors"
+import (
+       "crypto/hmac"
+       "errors"
+       "fmt"
+)
 
 // Auth is implemented by an SMTP authentication mechanism.
 type Auth interface {
@@ -65,3 +69,29 @@ func (a *plainAuth) Next(fromServer []byte, more bool) ([]byte, error) {
        }
        return nil, nil
 }
+
+type cramMD5Auth struct {
+       username, secret string
+}
+
+// CRAMMD5Auth returns an Auth that implements the CRAM-MD5 authentication
+// mechanism as defined in RFC 2195.
+// The returned Auth uses the given username and secret to authenticate
+// to the server using the challenge-response mechanism.
+func CRAMMD5Auth(username, secret string) Auth {
+       return &cramMD5Auth{username, secret}
+}
+
+func (a *cramMD5Auth) Start(server *ServerInfo) (string, []byte, error) {
+       return "CRAM-MD5", nil, nil
+}
+
+func (a *cramMD5Auth) Next(fromServer []byte, more bool) ([]byte, error) {
+       if more {
+               d := hmac.NewMD5([]byte(a.secret))
+               d.Write(fromServer)
+               s := make([]byte, 0, d.Size())
+               return []byte(fmt.Sprintf("%s %x", a.username, d.Sum(s))), nil
+       }
+       return nil, nil
+}

diff --git a/src/pkg/net/smtp/smtp_test.go b/src/pkg/net/smtp/smtp_test.go
index d4e9c38bf466b842561bc66a29ed4597086ae0e0..ce88782053172cae38fdb5a7b9843f4a74e08a85 100644 (file)
--- a/src/pkg/net/smtp/smtp_test.go
+++ b/src/pkg/net/smtp/smtp_test.go
@@ -23,6 +23,7 @@ type authTest struct {
 var authTests = []authTest{
        {PlainAuth("", "user", "pass", "testserver"), []string{}, "PLAIN", []string{"\x00user\x00pass"}},
        {PlainAuth("foo", "bar", "baz", "testserver"), []string{}, "PLAIN", []string{"foo\x00bar\x00baz"}},
+       {CRAMMD5Auth("user", "pass"), []string{"<123456.1322876914@testserver>"}, "CRAM-MD5", []string{"", "user 287eb355114cf5c471c26a875f1ca4ae"}},
 }
 
 func TestAuth(t *testing.T) {