One Hat Cyber Team

View File Name : Debugging.Authentication.txt

Debugging Authentication
========================

The most important thing to do is to set 'auth_debug=yes', and preferrably also
'auth_debug_passwords=yes'. After that you'll see in the logs exactly what
dovecot-auth is doing, and that should help you to fix the problem.

PLAIN SASL mechanism
--------------------

With IMAP and POP3 it's easy to log in manually using the IMAP's LOGIN command
or POP3's USER and PASS commands (see <TestInstallation.txt> and
<TestPop3Installation.txt> for details), but with SMTP AUTH you'll need to use
PLAIN authentication mechanism, which requires you to build a base64-encoded
string in the correct format. The PLAIN authentication is also used internally
by both IMAP and POP3 to authenticate to dovecot-auth, so you see it in the
debug logs.

The PLAIN mechanism's authentication format is: <authorization ID> NUL
<authentication ID> NUL <password>. Authorization ID is the username who you
want to log in as, and authentication ID is the username whose password you're
giving. If you're not planning on doing a <master user login>
[Authentication.MasterUsers.txt], you can either set both of these fields to
the same username, or leave the authorization ID empty.

Encoding with mmencode
----------------------

printf(1) and mmencode(1) should be available on most Unix or GNU/Linux
systems. (If not, check with your distribution. GNU coreutils includes
printf(1), and metamail includes mmencode(1). In Debian, mmencode is called
mimencode(1).)

---%<-------------------------------------------------------------------------
$ printf 'username\0username\0password' | mmencode
dXNlcm5hbWUAdXNlcm5hbWUAcGFzc3dvcmQ=
---%<-------------------------------------------------------------------------

This string is what a client would use to attempt PLAIN authentication as user
"username" with password "password." With ''auth_debug_passwords=yes', it would
appear in your logs.

Decoding with mmencode
----------------------

You can use mmencode -u to interpret the encoded string pasted into stdin as
follows:

---%<-------------------------------------------------------------------------
# mmencode -u
bXl1c2VybmFtZUBkb21haW4udGxkAG15dXNlcm5hbWVAZG9tYWluLnRsZABteXBhc3N3b3Jk<CR>
myusername@domain.tldmyusername@domain.tldmypassword<CTRL-D>
#
---%<-------------------------------------------------------------------------

You should see the correct user address (twice) and password.  The null bytes
won't display.

Encoding with Perl
------------------

Unfortunately, mmencode on FreeBSD chokes on "\0".  As an alternate, if you
have MIME::Base64 on your system, you can use a perl statement to do the same
thing:

---%<-------------------------------------------------------------------------
perl -MMIME::Base64 -e 'print
encode_base64("myusername\@domain.tld\0myusername\@domain.tld\0mypassword");'
---%<-------------------------------------------------------------------------

As mmencode -u doesn't encounter any "\0" you can still do:

---%<-------------------------------------------------------------------------
perl -MMIME::Base64 -e 'print
encode_base64("myusername\@domain.tld\0myusername\@domain.tld\0mypassword");' |
mmencode -u
---%<-------------------------------------------------------------------------

to check that you have encoded correctly.

Encoding with Python
--------------------

With python you can do:

---%<-------------------------------------------------------------------------
python -c "import base64;
print(base64.encodestring('myusername@domain.tld\0myusername@domain.tld\0mypassword'));"
---%<-------------------------------------------------------------------------

(This file was created from the wiki on 2019-06-19 12:42)