Post to team as a different user

When I use the team messaging create post endpoint, it posts a message with my extension as the author. Is it possible to make the author of the post a different extension user, one made specifically for using the API? The documentation doesn't seem to show a parameter for specifying author of the post. If it is always the "logged in" user, is there a way to change that user? I'm using JWT authorization flow and Node.js client libraries.

Here is my current code:

async function create_post() {
    try {
        var resp = await platform.post('/restapi/v1.0/glip/chats/chatid/posts', {
            text: 'Testing...'
        });
        var jsonObj = await resp.json();
        console.log("Post Created");
        console.log(jsonObj);
    } catch(e) {
        console.log(e.message);
    }
}