github.com/tcnksm/go@v0.0.0-20141208075154-439b32936367/src/net/smtp/auth.go (about)

     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.
    48  // The returned Auth uses the given username and password to authenticate
    49  // on TLS connections to host and act as identity. Usually identity will be
    50  // left blank to act as username.
    51  func PlainAuth(identity, username, password, host string) Auth {
    52  	return &plainAuth{identity, username, password, host}
    53  }
    54  
    55  func (a *plainAuth) Start(server *ServerInfo) (string, []byte, error) {
    56  	if !server.TLS {
    57  		advertised := false
    58  		for _, mechanism := range server.Auth {
    59  			if mechanism == "PLAIN" {
    60  				advertised = true
    61  				break
    62  			}
    63  		}
    64  		if !advertised {
    65  			return "", nil, errors.New("unencrypted connection")
    66  		}
    67  	}
    68  	if server.Name != a.host {
    69  		return "", nil, errors.New("wrong host name")
    70  	}
    71  	resp := []byte(a.identity + "\x00" + a.username + "\x00" + a.password)
    72  	return "PLAIN", resp, nil
    73  }
    74  
    75  func (a *plainAuth) Next(fromServer []byte, more bool) ([]byte, error) {
    76  	if more {
    77  		// We've already sent everything.
    78  		return nil, errors.New("unexpected server challenge")
    79  	}
    80  	return nil, nil
    81  }
    82  
    83  type cramMD5Auth struct {
    84  	username, secret string
    85  }
    86  
    87  // CRAMMD5Auth returns an Auth that implements the CRAM-MD5 authentication
    88  // mechanism as defined in RFC 2195.
    89  // The returned Auth uses the given username and secret to authenticate
    90  // to the server using the challenge-response mechanism.
    91  func CRAMMD5Auth(username, secret string) Auth {
    92  	return &cramMD5Auth{username, secret}
    93  }
    94  
    95  func (a *cramMD5Auth) Start(server *ServerInfo) (string, []byte, error) {
    96  	return "CRAM-MD5", nil, nil
    97  }
    98  
    99  func (a *cramMD5Auth) Next(fromServer []byte, more bool) ([]byte, error) {
   100  	if more {
   101  		d := hmac.New(md5.New, []byte(a.secret))
   102  		d.Write(fromServer)
   103  		s := make([]byte, 0, d.Size())
   104  		return []byte(fmt.Sprintf("%s %x", a.username, d.Sum(s))), nil
   105  	}
   106  	return nil, nil
   107  }