We have some questions about the required behaviour of the expiry date option for user and group shares (and the same principles should probably apply for public link shares)

1. When the "expiry date" options are not enabled at all, and the sharing API is used to create or modify a share and specifies an expiry date, what should happen?
   a) respond with a 4nn status code and do not do the action
   b) respond with a 2nn status code, create or modify the share using the other parameters provided, and just ignore the expiry date in the request
   c) respond with a 2nn status code, create or modify the share including setting an expiry date on the share - but the expiry date will be ineffective (because later processing will never check the expiry date
   d) or ???
   Note: public links seem to do (c) at the moment - so we can consider if their behaviour should be adjusted to (a)
   See issue expireDate can be specified when the option for expireDate is not enabled #36568

2. When the "expiry date" options are enabled, and there is a default expiry date, and a sharing API request comes without explicit mention of an expiry date then:
   a) the default expiry date should be calculated and set, and the response will include an expiry date attribute (that was not in the request)
   b) do not set an expiry date (unless it is enforced)

3. When the "expiry date" options have been enabled for a while, and there are share in the system with expiry dates. Then the admin disables the expiry date options:
   a) any expiry dates on existing shares continue to be enforced (but are not displayed in the UI, or in API requests for share info)
   b) any expiry dates on existing shares continue to be displayed and enforced
   c) expiry dates on existing shares "hang around" in the database but are not displayed or enforced any more (they "hang around" so that if the admin clicks the "expiry date" option on again in 10 minutes, then the existing expiry will not all be lost)
   d) expiry dates on existing shares are all removed permanently (so they do not come back when the "expiry date" option is enabled again

4. When admin reduces the enforced maximum expiry date:
   a) existing shares with expiry dates beyond the new maximum stay as they are
   b) existing shares with expiry dates beyond the new maximum get their expiry date reduced

5. If the admin sets the default expiry date to 0 days (and they could enforce that also):
   a) it means shares created today will expire at the end of the day
   b) 0 is not allowed - see issue default expire date config parameters can be set to 0 days #36569
   c) ???