we want (A-USER) to add events into a shared (with us) calendar of another user (B-USER).
in the https://outlook.office365.com/ews/odata/Me/Calendars list there aren\'t
Thanks for your interest in Office 365 REST APIs! At present we only allow access to mail, calendar and contacts belonging to the authenticated user. So, your scenario of making changes to a shared calendar is not supported at this time. Access to resources belonging to other users e.g. shared calendar is on our roadmap to support but we don't yet have a timeframe to share with you.
In the meantime, you can use our Exchange Web Services SOAP API to implement your scenario. If you are using .NET, then we recommend you use EWS Managed API to make the EWS calls and if you are using Java, we recommend you use EWS Java API to do the same. See here for info on how to create appointments on a calendar using EWS Managed API or raw SOAP request/response.
Hope that helps ...
Thanks,
Venkat