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-rw-r--r--src/net/smtp/auth.go110
1 files changed, 110 insertions, 0 deletions
diff --git a/src/net/smtp/auth.go b/src/net/smtp/auth.go
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+// Copyright 2010 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 smtp
+
+import (
+ "crypto/hmac"
+ "crypto/md5"
+ "errors"
+ "fmt"
+)
+
+// Auth is implemented by an SMTP authentication mechanism.
+type Auth interface {
+ // Start begins an authentication with a server.
+ // It returns the name of the authentication protocol
+ // and optionally data to include in the initial AUTH message
+ // sent to the server. It can return proto == "" to indicate
+ // that the authentication should be skipped.
+ // If it returns a non-nil error, the SMTP client aborts
+ // the authentication attempt and closes the connection.
+ Start(server *ServerInfo) (proto string, toServer []byte, err error)
+
+ // Next continues the authentication. The server has just sent
+ // the fromServer data. If more is true, the server expects a
+ // response, which Next should return as toServer; otherwise
+ // Next should return toServer == nil.
+ // If Next returns a non-nil error, the SMTP client aborts
+ // the authentication attempt and closes the connection.
+ Next(fromServer []byte, more bool) (toServer []byte, err error)
+}
+
+// ServerInfo records information about an SMTP server.
+type ServerInfo struct {
+ Name string // SMTP server name
+ TLS bool // using TLS, with valid certificate for Name
+ Auth []string // advertised authentication mechanisms
+}
+
+type plainAuth struct {
+ identity, username, password string
+ host string
+}
+
+// PlainAuth returns an Auth that implements the PLAIN authentication
+// mechanism as defined in RFC 4616. The returned Auth uses the given
+// username and password to authenticate to host and act as identity.
+// Usually identity should be the empty string, to act as username.
+//
+// PlainAuth will only send the credentials if the connection is using TLS
+// or is connected to localhost. Otherwise authentication will fail with an
+// error, without sending the credentials.
+func PlainAuth(identity, username, password, host string) Auth {
+ return &plainAuth{identity, username, password, host}
+}
+
+func isLocalhost(name string) bool {
+ return name == "localhost" || name == "127.0.0.1" || name == "::1"
+}
+
+func (a *plainAuth) Start(server *ServerInfo) (string, []byte, error) {
+ // Must have TLS, or else localhost server.
+ // Note: If TLS is not true, then we can't trust ANYTHING in ServerInfo.
+ // In particular, it doesn't matter if the server advertises PLAIN auth.
+ // That might just be the attacker saying
+ // "it's ok, you can trust me with your password."
+ if !server.TLS && !isLocalhost(server.Name) {
+ return "", nil, errors.New("unencrypted connection")
+ }
+ if server.Name != a.host {
+ return "", nil, errors.New("wrong host name")
+ }
+ resp := []byte(a.identity + "\x00" + a.username + "\x00" + a.password)
+ return "PLAIN", resp, nil
+}
+
+func (a *plainAuth) Next(fromServer []byte, more bool) ([]byte, error) {
+ if more {
+ // We've already sent everything.
+ return nil, errors.New("unexpected server challenge")
+ }
+ 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.New(md5.New, []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
+}