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annotate auth.go @ 0:6369453d47a3

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Initial revision
author Guido Berhoerster <guido+managesieve@berhoerster.name>
date Thu, 15 Oct 2020 09:11:05 +0200
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1 // Copyright (C) 2020 Guido Berhoerster <guido+managesieve@berhoerster.name>
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2 //
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3 // Permission is hereby granted, free of charge, to any person obtaining
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4 // a copy of this software and associated documentation files (the
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5 // "Software"), to deal in the Software without restriction, including
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6 // without limitation the rights to use, copy, modify, merge, publish,
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7 // distribute, sublicense, and/or sell copies of the Software, and to
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8 // permit persons to whom the Software is furnished to do so, subject to
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9 // the following conditions:
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10 //
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11 // The above copyright notice and this permission notice shall be included
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12 // in all copies or substantial portions of the Software.
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13 //
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14 // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
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15 // EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
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16 // MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
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17 // IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
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18 // CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
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19 // TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
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20 // SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
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21
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22 package managesieve
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23
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24 import (
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25 "errors"
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26 "fmt"
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27 )
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28
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29 // this API is inspired by the SASL authentication API in net/smtp
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30
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31 // ServerInfo stores information about the ManageSieve server.
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32 type ServerInfo struct {
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33 Name string // hostname of the server
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34 TLS bool // whether a verified TLS connection is used
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35 Auth []string // authentication methods advertised in capabilities
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36 }
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37
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38 // Check whether the server supports the wanted SASL authentication mechanism.
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39 func (s *ServerInfo) HaveAuth(wanted string) bool {
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40 for _, m := range s.Auth {
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41 if m == wanted {
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42 return true
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43 }
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44 }
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45 return false
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46 }
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47
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48 type Auth interface {
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49 // Initiate SASL authentication. A non-nil response will be sent in
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50 // response to an empty challenge from the server if mandated by the
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51 // authentication mechanism. The name of the SASL authentication
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52 // mechanism is returned in mechanism. If an error is returned SASL
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53 // authentication will be aborted and an AuthenticationError will be
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54 // returned to the caller.
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55 Start(server *ServerInfo) (mechanism string, response []byte, err error)
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56 // Handle a challenge received from the server, if more is true the
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57 // server expects a response, otherwise the response should be nil. If
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58 // an error is returned SASL authentication will be aborted and an
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59 // AuthenticationError will be returned to the caller.
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60 Next(challenge []byte, more bool) (response []byte, err error)
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61 }
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62
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63 var (
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64 // ErrPlainAuthNotSupported is returned if the server does not support
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65 // the SASL PLAIN authentication mechanism.
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66 ErrPlainAuthNotSupported = errors.New("the server does not support PLAIN authentication")
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67 // ErrPlainAuthTLSRequired is returned when the SASL PLAIN
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68 // authentication mechanism is used without TLS against a server other
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69 // than localhost.
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70 ErrPlainAuthTLSRequired = errors.New("PLAIN authentication requires a TLS connection")
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71 )
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72
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73 // HostNameVerificationError is returned when the hostname which was passed to
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74 // the Auth implementation could not be verified against the TLS certificate.
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75 type HostNameVerificationError struct {
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76 ExpectedHost, ActualHost string
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77 }
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78
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79 func (e *HostNameVerificationError) Error() string {
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80 return fmt.Sprintf("host name mismatch: %s != %s", e.ActualHost,
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81 e.ExpectedHost)
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82 }
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83
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84 type plainAuth struct {
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85 identity string
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86 username string
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87 password string
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88 host string
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89 }
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90
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91 func (a *plainAuth) Start(server *ServerInfo) (string, []byte, error) {
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92 if !server.HaveAuth("PLAIN") {
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93 return "PLAIN", nil, ErrPlainAuthNotSupported
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94 }
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95
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96 // enforce TLS for non-local servers in order to avoid leaking
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97 // credentials via unencrypted connections or DNS spoofing
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98 if !server.TLS && server.Name != "localhost" &&
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99 server.Name != "127.0.0.1" && server.Name != "::1" {
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100 return "PLAIN", nil, ErrPlainAuthTLSRequired
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101 }
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102
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103 // verify server hostname before sending credentials
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104 if server.Name != a.host {
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105 return "PLAIN", nil,
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106 &HostNameVerificationError{a.host, server.Name}
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107 }
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108
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109 resp := []byte(a.identity + "\x00" + a.username + "\x00" + a.password)
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110 return "PLAIN", resp, nil
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111 }
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112
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113 func (a *plainAuth) Next(challenge []byte, more bool) ([]byte, error) {
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114 return nil, nil
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115 }
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116
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117 // PlainAuth provides an Auth implementation of SASL PLAIN authentication as
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118 // specified in RFC 4616 using the provided authorization identity, username
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119 // and password. If the identity is an empty string the server will derive an
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120 // identity from the credentials.
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121 func PlainAuth(identity, username, password, host string) Auth {
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122 return &plainAuth{identity, username, password, host}
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123 }