I have been struggling a lot as impersonation step is missing in 2013 workflow. I tried doing the same using 'App step' by making use of API's. When try hitting this API from within the workflow no change in permissions reflects in the library for the item. When I try doing this using fiddler or directly from the SharePoint site (using script editor), this happens:
API : https://xyz.sharepoint.com/helpdesk/_api/Web/Lists/GetByTitle('Draft')/Items(35)/roleassignments(21)
Purpose : For deleting the the role associated with the same item for user ID '21'.
Response from server is : status of 403 (FORBIDDEN)
I am clueless as of now. Other than this I have provided my workflow with all app permissions and enabled the app step too. Any help would be much appreciated.