On 26.9.2013, at 10.01, Nicolay Vizovitin vizovitin@gmail.com wrote:
I'm about to start developing authentication/password-scheme module for Dovecot. So I would like to get some advice before actually committing to doing things in particular way. Hope somebody will be able to help me :)
For the record, I am currently targeting latest stable Dovecot version 2.2.5.
I have an SQL DB with mail users' authentication data. Passwords are stored either encrypted via system crypt(3) or ciphered with some custom algorithm (think something symmetrical like AES, so passwords can be decrypted into plain form). I want to use this DB as both userdb and passdb backend. The issue, of course, is with ciphered passwords support.
- Is it feasible to just implement a new password scheme for ciphered passwords support and still use stock passdb driver in Dovecot for SQL DB access?
Plugins can implement new password schemes. http://dovecot.org/patches/password-scheme-lmpass.c is an example, although I'm not sure if it compiles with v2.2.
So that passwords in this scheme would be treated as PLAIN (in a sense that both cleartext and shared secret authentication methods would work).
You could do that in a slightly ugly way by setting password_generate=plain_generate(), so password_scheme_is_alias() returns TRUE for that.
- Provided I implement custom password scheme for ciphered passwords, what is the best way to be capable to perform authentication against both ciphered and encrypted passwords? Ciphered and encrypted passwords are stored in different fields of SQL table (one of them is NULL when the other one is set). a) Do I define two passdb clauses with their own default_pass_scheme (equal to my new scheme or CRYPT for encrypted passwords) and use fallback to effectively check both of them? b) Do I modify SQL query so that it prefixes existing password with correct scheme (I'm not sure this will be easy enough to do)?
By "ciphered" I understand you mean encrypted, and by "encrypted" you mean hashed.. Scheme prefix would work, mysql and postgresql have complex enough string manipulation functions to make this possible I think.
- Is it mandatory to provide password generation routine for custom password scheme? When it will be used?
doveadm pw command would use it for example. But as mentioned, you should set it to plain_generate.
- Maybe it's better to just implement a plugin that serves as both userdb and passdb driver (in other words a kind of generic authentication module)? What are advantages and disadvantages of each method - custom password scheme + stock SQL driver VS. custom userdb and passdb driver? Fortunately, I already have all the required credentials lookup and verification code. So in any case the question is only in figuring out suitable Dovecot APIs and integrating the existing code.
Implementing yet another sql passdb sounds like quite a lot of work.
- Somewhat unrelated question: what is the best way to test IMAP (and maybe POP3 as well) server performance and compare it to another server? I'm interested in both login performance (the part I will influence) and performance with many mails in mailbox. I heard imaptest is suitable for this task. Are there any recipes or example testing scenarios you might share? ;)
There are only bad non-realistic benchmarks available currently. With imaptest you can easily test the login performance though:
imaptest user=test%d.%d - select=0 clients=100