Redmine

Hello,

I am integrating redmine issues via the REST API in an application to propose to my users to create issues and follow up their issues.
I would like to have only one master API key to handle all requests (a key mapped on a user with appropriate admin rights).
It works just fine to create, update, delete users, get issue list.

When it comes to create issues there is a problem.
Each of my users has a redmine user id, and I would like this redmine user id to be set as the new issue author id, while using the master API key to create the issue.
But the issue is created with the author being the master user (who's API key is used for the request).

In the manual it is said that the following tags can be used in the create issue request:

description
category_id
assigned_to_id - ID of the user to assign the issue to (currently no mechanism to assign by name)
status_id
parent_issue_id - ID of the parent issue
...

I would like to know what is hidden being those ...

Is the author_id not an option?
Is the behavior I describe normal?

Thanks