Populate drop down list items from external data source

Hi,

We have a requirement to populate a ribbon dropdown's list items, from a SharePoint list. For example; when clicked, the highlighted 'Document Generation' button should display list items retrieved from a SharePoint list, in particular it should display the values from the "Name" field in the SharePoint list.

It is possible for us to create an API endpoint that returns all of the 'Name' values from the SharePoint list, but I'm not sure if it's possible for the Document Generation button to retrieve those values on click, and subsequently display those values as list item elements in the dropdown?

Is there a simpler or alternative solution that I am missing? 

Thanks in advance for any suggestions.