...
Run Format

Source file src/net/smtp/auth.go

Documentation: net/smtp

     1  // Copyright 2010 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package smtp
     6  
     7  import (
     8  	"crypto/hmac"
     9  	"crypto/md5"
    10  	"errors"
    11  	"fmt"
    12  )
    13  
    14  // Auth is implemented by an SMTP authentication mechanism.
    15  type Auth interface {
    16  	// Start begins an authentication with a server.
    17  	// It returns the name of the authentication protocol
    18  	// and optionally data to include in the initial AUTH message
    19  	// sent to the server. It can return proto == "" to indicate
    20  	// that the authentication should be skipped.
    21  	// If it returns a non-nil error, the SMTP client aborts
    22  	// the authentication attempt and closes the connection.
    23  	Start(server *ServerInfo) (proto string, toServer []byte, err error)
    24  
    25  	// Next continues the authentication. The server has just sent
    26  	// the fromServer data. If more is true, the server expects a
    27  	// response, which Next should return as toServer; otherwise
    28  	// Next should return toServer == nil.
    29  	// If Next returns a non-nil error, the SMTP client aborts
    30  	// the authentication attempt and closes the connection.
    31  	Next(fromServer []byte, more bool) (toServer []byte, err error)
    32  }
    33  
    34  // ServerInfo records information about an SMTP server.
    35  type ServerInfo struct {
    36  	Name string   // SMTP server name
    37  	TLS  bool     // using TLS, with valid certificate for Name
    38  	Auth []string // advertised authentication mechanisms
    39  }
    40  
    41  type plainAuth struct {
    42  	identity, username, password string
    43  	host                         string
    44  }
    45  
    46  // PlainAuth returns an Auth that implements the PLAIN authentication
    47  // mechanism as defined in RFC 4616. The returned Auth uses the given
    48  // username and password to authenticate to host and act as identity.
    49  // Usually identity should be the empty string, to act as username.
    50  //
    51  // PlainAuth will only send the credentials if the connection is using TLS
    52  // or is connected to localhost. Otherwise authentication will fail with an
    53  // error, without sending the credentials.
    54  func PlainAuth(identity, username, password, host string) Auth {
    55  	return &plainAuth{identity, username, password, host}
    56  }
    57  
    58  func isLocalhost(name string) bool {
    59  	return name == "localhost" || name == "127.0.0.1" || name == "::1"
    60  }
    61  
    62  func (a *plainAuth) Start(server *ServerInfo) (string, []byte, error) {
    63  	// Must have TLS, or else localhost server.
    64  	// Note: If TLS is not true, then we can't trust ANYTHING in ServerInfo.
    65  	// In particular, it doesn't matter if the server advertises PLAIN auth.
    66  	// That might just be the attacker saying
    67  	// "it's ok, you can trust me with your password."
    68  	if !server.TLS && !isLocalhost(server.Name) {
    69  		return "", nil, errors.New("unencrypted connection")
    70  	}
    71  	if server.Name != a.host {
    72  		return "", nil, errors.New("wrong host name")
    73  	}
    74  	resp := []byte(a.identity + "\x00" + a.username + "\x00" + a.password)
    75  	return "PLAIN", resp, nil
    76  }
    77  
    78  func (a *plainAuth) Next(fromServer []byte, more bool) ([]byte, error) {
    79  	if more {
    80  		// We've already sent everything.
    81  		return nil, errors.New("unexpected server challenge")
    82  	}
    83  	return nil, nil
    84  }
    85  
    86  type cramMD5Auth struct {
    87  	username, secret string
    88  }
    89  
    90  // CRAMMD5Auth returns an Auth that implements the CRAM-MD5 authentication
    91  // mechanism as defined in RFC 2195.
    92  // The returned Auth uses the given username and secret to authenticate
    93  // to the server using the challenge-response mechanism.
    94  func CRAMMD5Auth(username, secret string) Auth {
    95  	return &cramMD5Auth{username, secret}
    96  }
    97  
    98  func (a *cramMD5Auth) Start(server *ServerInfo) (string, []byte, error) {
    99  	return "CRAM-MD5", nil, nil
   100  }
   101  
   102  func (a *cramMD5Auth) Next(fromServer []byte, more bool) ([]byte, error) {
   103  	if more {
   104  		d := hmac.New(md5.New, []byte(a.secret))
   105  		d.Write(fromServer)
   106  		s := make([]byte, 0, d.Size())
   107  		return []byte(fmt.Sprintf("%s %x", a.username, d.Sum(s))), nil
   108  	}
   109  	return nil, nil
   110  }
   111  

View as plain text