[Dovecot] Additional passdb result status

[Jürgen Pabel]

Dear Dovecot-Team,

I am implementing a plugin (for the pop3/imap process) that requires
some data to provided from the authentication phase (a derivative of the
password). For that, I have now implemented a passdb plugin that
generates this data and I would like to "pass" this data down to the
mail process (pop3/imap) via extra_fields in the reply of the
authentication. The general idea is that my custom passdb plugin
calculates the data, sets the extra_field and returns some error
(authentication was not successful) so that the "real" passdb backend
can be invoked to "really" validate the authentication data. 

However, in auth_request_handle_passdb_callback() the extra_fields are
reseted unless the return code is PASSDB_RESULT_USER_DISABLED. But if
that return code is used then any following passdb's aren't invoked any
more - which makes sense with respect to user authenticiation. I would
therefore like to propose that some IGNORE/CONTINUE-status to be
introduced in auth/passdb.h, that would be handled in that extra_fields
and possible other values are not reseted in order to allow such
propagation of data from authentication process down to the mail process
(which could be extracted from the reply string by parsing it).

As a further implementation alternative (to the parsing of the reply
string), I also propose that some new "environment" item be introduced
(in auth_request) in order to allow such data passing in a generic
manner. 

I hope you consider my proposal to be reasonable. If desired, I could
implement this myself and provide a patch for merging (based on 2.0.x).
If my proposal is generally unfavored, it would be great if any
alternative approaches for my situation were suggested. Thanks.

Regards,
Jürgen

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