[Freeipa-devel] [Update]Time-Based Account Policies

Wed Nov 11 08:24:18 UTC 2015

On 11/05/2015 06:17 PM, Petr Spacek wrote:
> On 4.11.2015 15:20, Martin Basti wrote:
>
>> Hello,
>>
>> we (Standa and I) had offline discussion and I proposed following idea:
>>
>> 1) create new entry in LDAP for "time rule" instead of adding the time rule
>> string directly into HBACRule.
>> This will allow to reuse time rules among various HBAC Rules (and maybe in
>> future with sudo rules, etc.)
>> HBACrule gets only reference to time rule entry stored in LDAP db.
> Good idea! I can see time rule entry 'working hours in Brno office' which is
> linked to relevant HBAC rules.
This seems like a good idea. However, it might be a bit messy to have 
even the least significant rules stored in separate objects. But I 
agree. It brings some questions, though.
Where would be a good spot to store these time rules? Should they be 
able to form groups? Should such an object be able to hold more time 
policies strings and exceptions, as it does now, or would it be better 
to set that in the respective HBAC rule?
>
>> 2) Do not create a new time format, just reuse iCal (parts of iCal we need),
>> to store time rule in LDAP in "time rule" entry
>> (Or is possible to not store the values just as one string, we can use
>> different attributes to store separate values, iCal can be used as export and
>> import format)
> I very much agree with re-using iCal! We have sufficient number of custom
> parsers already ;-)
>
> Speaking about custom LDAP format, I do not think that it is a good idea. It
> would prevent us from using iCal parsers and generators and we would risk that
> our custom LDAP format will not be flexible enough.
>
> For these reasons I would go with 1 iCal string which can be fed into any
> standard-compliant iCal library.
I was thinking long and hard about actually using the iCalendar format 
for this purpose, ever since the 'repeat' keyword was supposed to be 
included in the language. However, as I mentioned some time ago, the 
iCalendar format recurrences are OK when it comes to recurring events 
but I am not sure about them being very suitable for describing time 
policies.

Let me do a comparison of the options. I will take in question only the 
RRULE (and possibly PERIOD) part of the iCalendar format. Having the 
whole iCalendar format involved along with its parsing C library seemed 
to be a no-go for SSSD some 6 months ago and I can imagine such feelings 
persist.

----------------------------
Some iCalendar cons:

1) It is hard to represent continuous time of a day ranges
There does not seem to be an easy equivalent to e.g. 'timeofday= 
0730~1100, 1200~1615'. The easiest way to do this in iCalendar would be 
to have 2 rules of the form:

DTSTART: 19700101T073000
DTEND: 19700101T110000
RRULE: FREQ=DAILY; INTERVAL=1

DTSTART: 19700101T120000
DTEND: 19700101T161500
RRULE: FREQ=DAILY; INTERVAL=1

If you were setting some more difficult policy, there would have to be a 
lot of duplicity in each of such rules.

2) All iCalendar events have to have a fixed starting point
There must always be a check against the interval and the starting point.

3) There are no ranges
e.g. 'dayofyear=2-50, 100-125' would translate to

DTSTART:19700101T000000
RRULE: FREQ=SECONDLY; INTERVAL=1; 
BYYEARDAY=2,3,4,5,6,7,8,9,10,11,...50,100,101,102,...

4) There is no way to list specific years in which the HBAC rule should 
apply.

5) COUNT parameter makes you generate all previous events before you are 
able to tell if the current one actually applies.
Imagine COUNT being a big number and an event that hardly ever happens. 
Imagine current time to fall into the last event.

6) The event descriptions are not so intuitive
There would probably have to be better conversion system at least for 
CLI when user wants to set time ranges of access allowed times so that 
we can consider it good UX.

I am not mentioning the lack of weekofmonth in iCal as I would rather 
drop it from the current solution, too.
----------------------------
On the other hand, there are also some big pros for iCalendar.

1) It is a standard. It behaves in a known and described manner.
2)  By proper use of BYSETPOS of RRULE, it is able to describe some 
specific situations, e.g. last workday of a month. This is not possible 
in the current language.
3) Easier setting of absolute time ranges using the PERIOD property 
(although this could probably be easily solved by a minor addition to 
the current solution).
4) A GUI for setting RRULEs already exists.

ad 4) The GUI, however, hides some of the features of the language (e.g. 
the mentioned BYSETPOS) and is not suitable for setting time policies as 
is. Try, for example, setting a policy "allow access from 7:00 to 16:00 
(no break of the interval as iCalendar does not know it) every first 
Monday through Friday of a month for the first half of every year".

In current language:

timeofday=0700~1600 dayofmonth=1~7 dayofweek=1~5 monthofyear=1~6

In iCalendar RRULE:

DTSTART: 19700101T070000
DTEND: 19700101T160000
RRULE: FREQ=YEARLY; BYMONTH=1,2,3,4,5,6;BYDAY=1MO,1TU,1WE,1TH,1FR
----------------------------

Hopefully, this was a thorough walk-through of the pros and cons of both 
approaches. I believe I stayed clear of any sentiment to the work I did 
of which a big part could come in vain if we moved to iCalendar format. 
Please correct me if I haven't.

I wonder if we want to have someone from SSSD in this discussion, too.
>
>> 3) We may provide nice CLI and webUI to construct/show "time rule", this may
>> be more user friendly than just passing the string containing time data to
>> HBAC rule.
> This is going to be the same as in any calendaring system. Just look to
> Thunderbird "New Event" dialog.
>
Please, see my comments on the GUI in ad 4). On the other hand to the 
comments - there is at least something done in iCalendar GUI that we 
could use rather than coining out a whole new GUI for time policies.

--
Standa
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