Hello Lars,
I don’t know vTiger but generally speaking there are multiple ways how you can approach this:
If vTiger is able to send invites, you can use the mr-processing capabilities to automatically accept (and for example automatically decline by collision, etc.), you can find the MR setup here:
https://documentation.kopano.io/kopanocore_administrator_manual/user_management.html#resource-configuration
Generally speaking, this approach limits you to resource mailboxes and this might not be what you want.
You can use python (and python-kopano) to create a script for example to import these events on a regular basis from vTiger. Again, I don’t know the exact specifics on vTiger side, but I can give you an entry point with python-kopano here: https://documentation.kopano.io/kopano_python_kopano/
You could use our experimental REST interface we are working on which is deemed also to be used for such use cases in the future. We are still working on documentation, but I can tell you for the moment the best entrypoints are https://stash.kopano.io/projects/KC/repos/kopanocore/browse/ECtools/rest and https://github.com/microsoftgraph/microsoft-graph-docs/tree/master/api-reference/v1.0/api to have a look at and how to get going. You will need some skills in API development though to be able to work on it for the moment. We can tell for the moment that calendaring is in a good shape and should fulfill your requirements already today - if you should hit any obstacles please let us know.
Hope this helps to get started.
- mike