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Dovecot authentication protocol v1.0
author Timo Sirainen <tss@iki.fi>
date Fri, 22 Oct 2004 16:44:03 +0300
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1 Dovecot Authentication Protocol v1.0
2
3
4 General
5 -------
6
7 This is a line based protocol. Each line is a command which ends with an LF
8 character. The maximum line length isn't defined, but it's currently
9 expected to fit into 8192 bytes. Authentication mechanism specific data
10 transfers are the largest single parameters.
11
12 Each command is in format:
13
14 <command name> TAB <parameters separated with TAB>
15
16 Parameters are split into required and optional parameters. Required
17 parameters aren't in any specific format, but optional parameters are
18 either booleans without a value, or a name=value pair. If optional parameter
19 name is unknown, the parameter should just be ignored.
20
21 Typical command looks like (without spaces):
22
23 command TAB param1 TAB param2 TAB optname=value TAB optboolean
24
25 There is no way to have TABs or LFs in parameters.
26
27
28 Client <-> Server
29 -----------------
30
31 Client is an untrusted authentication client process. It can serve one or
32 more users, so from user's point of view it's usually eg. IMAP or SMTP
33 server process.
34
35 Server is an authentication server process.
36
37 The connection starts by both client and server sending handshakes:
38
39 C: "VERSION" TAB <major> TAB <minor>
40 C: "SERVICE" TAB <service> (optional)
41 C: "CPID" TAB <pid>
42
43 S: "VERSION" TAB <major> TAB <minor>
44 S: "SPID" TAB <pid>
45 S: "CUID" TAB <pid>
46 S: "MECH" TAB <name> [TAB <parameters>] (multiple times)
47 S: "DONE"
48
49 Both client and server should check that they support the same major version
50 number. If they don't, the other side isn't expected to be talking the same
51 protocol and should be disconnected. Minor version can be ignored. This
52 document is version number 1.0.
53
54 CPID, SPID and specify client and server PIDs. They should be unique
55 identifiers for the specific process. UNIX process IDs are good choices.
56
57 CUID is a server process-specific unique connection identifier. It's
58 different each time a connection is established for the server.
59
60 CPID is used by master's REQUEST command.
61
62 SPID can be used by authentication client to tell master what server
63 process handled the authentication.
64
65 CUID is currently useful only for APOP authentication.
66
67 SERVICE command can be used to specify default service name for
68 authentication requests. If it's not set, each request must specify the
69 service separately.
70
71 DONE finishes the handshake from server. CPID finishes the handshake from
72 client.
73
74
75 Authentication Mechanisms
76 -------------------------
77
78 MECH command announces an available authentication SASL mechanism.
79 Mechanisms may have parameters giving some details about them:
80
81 - anonymous : Anonymous authentication
82 - plaintext : Transfers plaintext passwords
83 - dictionary : Subject to passive (dictionary) attack
84 - active : Subject to active (non-dictionary) attack
85 - forward-secrecy : Provides forward secrecy between sessions
86 - mutual-auth : Provides mutual authentication
87 - private : Don't advertise this as available SASL mechanism (eg. APOP)
88
89
90 Authentication Request
91 ----------------------
92
93 C: "AUTH" TAB <id> TAB <mechanism> [TAB <parameters>]
94
95 S1: "FAIL" TAB <id> [TAB <parameters>]
96 S2: "CONT" TAB <id> TAB <base64 data>
97 S3: "OK" TAB <id> [TAB <parameters>]
98
99 ID is a connection-specific unique request identifier. It must be a 32bit
100 number, so typically you'd just increment it by one.
101
102 AUTH parameters are:
103
104 - lip=<local ip> : Local IP - in standard string format,
105 - rip=<remote ip> : Remote IP - ie. for IPv4 127.0.0.1 and for IPv6 ::1
106 - service=<service> : Service name (eg. POP3, IMAP, SMTP)
107 - resp=<base64> : Initial response for authentication mechanism
108 - secured : Remote user has secured transport to auth client
109 (eg. localhost, SSL, TLS)
110 - ssl-valid-cert : Remote user has presented a valid SSL certificate.
111
112 FAIL parameters may contain "reason=.." parameter which should be sent to
113 remote user instead of a standard "Authentication failed" message. For
114 example "invalid base64 data" or "temporary internal failure". It should
115 NOT be used to give exact reason for authentication failure (ie. "user not
116 found" vs. "password mismatch").
117
118 CONT command means that the authentication continues, and more data is
119 expected from client to finish the authentication. Given base64 data should
120 be sent to client.
121
122 FAIL and OK may contain multiple unspecified parameters which
123 authentication client may handle specially. The only one specified here is
124 "user=<userid>" parameter, which should always be sent if userid is known.
125
126
127 Server <-> Master
128 -----------------
129
130 Master is a trusted process which may query results of previous client
131 authentication or information about a specific user. Master is optional and
132 in SMTP AUTH case it's not needed.
133
134 The connection starts by both server and master sending handshakes:
135
136 S: "VERSION" TAB <major> TAB <minor>
137 S: "SPID" TAB <pid>
138
139 M: "VERSION" TAB <major> TAB <minor>
140
141 Auth with client <-> server, both should check that the version numbers are
142 valid.
143
144 SPID can be used to let master identify the server process.
145
146
147 Master Requests
148 ---------------
149
150 M: "REQUEST" TAB <id> TAB <client-pid> TAB <client-id>
151 M: "USER" TAB <id> TAB <userid>
152 M: "DIE"
153
154 S: "NOTFOUND" TAB <id>
155 S: "FAIL" TAB <id> TAB <error message>
156 S: "USER" TAB <id> TAB <userid> [TAB <parameters>]
157
158 Master commands can request information about existing authentication
159 request, or about a specified user.
160
161 ID is a connection-specific unique request identifier. It must be a 32bit
162 number, so typically you'd just increment it by one.
163
164 DIE makes the server stop accepting new requests, and as soon as the
165 existing requests are finished, it kills itself.
166
167 NOTFOUND reply means that the request or user wasn't found. Master
168 shouldn't even try to send REQUEST commands for nonexisting requests, so if
169 it happens it means either a timeout caused by very high load, or client
170 lying to master about the request.
171
172 FAIL reply means an internal error occured. Usually either a configuration
173 mistake or temporary error caused by lost resource (eg. database down).
174
175 USER reply is sent if request succeeded. It can return parameters:
176
177 uid=<uid> : System user ID.
178 gid=<gid> : System group ID.
179 home=<dir> : Home directory.
180 chroot=<dir> : Chroot directory.
181 mail=<data> : Mail location.
182 system_user=<user> : System user name which can be used to get extra groups.
183 This will probably be replaced later by giving just
184 multiple gid fields.