1PAM::FAQ(3) User Contributed Perl Documentation PAM::FAQ(3)
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6 Authen::PAM::FAQ - Frequently-Asked Questions about Authen::PAM.
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9 perldoc Authen::PAM::FAQ
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12 This document is currently at version 0.05, as of May 4, 2005
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15 1. Can I authenticate a user non interactively?
16 Yes, you can although not in a very clean way. The PAM library has a
17 mechanism, in a form of a conversation function, to send and receive
18 text data from the user. For details of the format of the conversation
19 function consult the Authen::PAM manual. This function receives a list
20 of code/string pairs. There are two codes (PAM_TEXT_INFO and
21 PAM_ERROR_MSG) for displaying the associated string to the user and two
22 codes (PAM_ECHO_ON and PAM_ECHO_OFF) for getting input from the user.
23 As you can see the codes are rather general and you can not be
24 completely sure when you are asked for a user name and when for a
25 password. However, the common practice is that PAM_ECHO_ON is used for
26 a user name and PAM_ECHO_OFF is used for a password. So, what you can
27 do is to write your own conversation function which ignores the
28 PAM_TEXT_INFO and PAM_ERROR_MSG codes and returns the user name for the
29 code PAM_ECHO_ON and the password for the code PAM_ECHO_OFF. If you
30 pass the user name in the initialization function then usually you will
31 not be asked for it. Here is a simple example how to do this:
32 use Authen::PAM;
34 use POSIX qw(ttyname);
35 $service = "login";
37 $username = "foo";
38 $password = "bar";
39 $tty_name = ttyname(fileno(STDIN));
40 sub my_conv_func {
42 my @res;
43 while ( @_ ) {
44 my $code = shift;
45 my $msg = shift;
46 my $ans = "";
47 $ans = $username if ($code == PAM_PROMPT_ECHO_ON() );
49 $ans = $password if ($code == PAM_PROMPT_ECHO_OFF() );
50 push @res, (PAM_SUCCESS(),$ans);
52 }
53 push @res, PAM_SUCCESS();
54 return @res;
55 }
56 ref($pamh = new Authen::PAM($service, $username, \&my_conv_func)) ||
58 die "Error code $pamh during PAM init!";
59 $res = $pamh->pam_set_item(PAM_TTY(), $tty_name);
61 $res = $pamh->pam_authenticate;
62 print $pamh->pam_strerror($res),"\n" unless $res == PAM_SUCCESS();
63 The Authen::PAM module comes with a default conversation function which
65 you can find in the file PAM.pm.
66 2. Can I change a password non interactively?
68 All the discussion of the previous question also applies here. There
69 is however one serious complication. When changing a password it is
70 quite possible that the PAM library will send you at lest two
71 PAM_ECHO_OFF prompts - one for the old password and one or two for the
72 new one. Therefore, the first thing you should do is to see what
73 sequence of prompts is produced by your service. Then the conversation
74 function should include some state variable to distinguish the
75 different prompts. Here is an example:
76 use Authen::PAM;
78 $service = "passwd";
80 $username = "foo";
81 $oldpassword = "old_pass";
82 $newpassword = "new_pass";
83 sub my_conv_func {
85 my @res;
86 while ( @_ ) {
87 my $code = shift;
88 my $msg = shift;
89 my $ans = "";
90 $ans = $username if ($code == PAM_PROMPT_ECHO_ON() );
92 if ($code == PAM_PROMPT_ECHO_OFF() ) {
93 $ans = $oldpassword if ($state == 0);
94 $ans = $newpassword if ($state == 1);
95 $ans = $newpassword if ($state == 2);
96 $state++;
98 }
99 push @res, (PAM_SUCCESS(),$ans);
101 }
102 push @res, PAM_SUCCESS();
103 return @res;
104 }
105 ref($pamh = new Authen::PAM($service, $username, \&my_conv_func)) ||
107 die "Error code $pamh during PAM init!";
108 $state = 0;
110 $res = $pamh->pam_chauthtok;
111 print $pamh->pam_strerror($res),"\n" unless $res == PAM_SUCCESS();
112 If you are running the script as root then most likely you will not be
114 prompted for an old password. In this case you can simply return the
115 new password at the ECHO_OFF prompt.
116 The $msg variable contains the text of the input prompt which you can
118 use for additional test or for debugging purposes, e.g.
119 if ($code == PAM_PROMPT_ECHO_OFF() ) {
121 if ($state>=1 || $msg=~/new/i) { # are we asked for a new password
122 $ans = $newpassword;
123 } else {
124 $ans = $oldpassword;
125 }
126 $state++;
127 }
128 3. Why are the constants PAM_AUTHTOK and PAM_OLDAUTHTOK not avaliable?
130 The PAM_AUTHTOK and PAM_OLDAUTHTOK items can be used to pass
131 authentication tokens (passwords) from one module to another. However,
132 they are avaliable only to PAM modules and not to PAM applicatinos. If
133 you have a special setup in which you really need to preset the
134 password from the application (e.g. using a radius server) then you can
135 use the pam_set_authtok module avaliable from
136 <http://www.uni-hohenheim.de/~schaefer/linux/pam/pam_set_authtok.html>.
137
139 Authen::PAM
140
142 Nikolay Pelov <NIKIP at cpan.org>
143
145 Copyright (c) 1998-2005 Nikolay Pelov. All rights reserved. This file
146 is part of the Authen::PAM library. This library is free software; you
147 can redistribute it and/or modify it under the same terms as Perl
148 itself.
149perl v5.38.0 2023-07-20 PAM::FAQ(3)