Alfresco Content Services exposes a RESTful endpoint where you can retrieve the list of the users inside the system:
The endpoint URI is the following:
https://api-explorer.alfresco.com/alfresco/api/-default-/public/alfresco/versions/1/people
username and password of the endpoint are: admin/admin
Using the data returned from the endpoint you are requested to create a chips list to show a list of users