SPD Workflow: Adding user to group using REST throws Unauthorized error

Question

I have created a SharePoint 2013 Workflow. This workflow first checks whether a user exists in a sharepoint group for example My_SP_GROUP or not by using HTTP GET request. If user does not exists then it adds that user in My_SP_GROUP using HTTP POST request.

The problem I am facing is that for POST request I am getting unauthorized error message, but for GET request it works fine.

{"odata.error":{"code":"-2147024891, System.UnauthorizedAccessException","message":{"lang":"en-US","value":"Access denied. You do not have permission to perform this action or access this resource."}}}

From SPO UI, I am able to add user in MY_SP_Group. I have followed this very nice article.

Answer 1

When you set permissions for the app step did you set the scope to site collection?
The site groups cannot be edited from a web scope.
Note that there is no web in the scope below

<AppPermissionRequests>
    <AppPermissionRequest Scope="http://sharepoint/content/sitecollection" Right="FullControl" />
</AppPermissionRequests>

Thanks to Fabian Williams
http://www.fabiangwilliams.com/2014/06/19/gotcha-on-sharepoint-designer-workflows-in-app-step/