I struck and interesting issue on a SharePoint 2013 web application. I had configured the site to allow anonymous access but started getting multiple login prompts when after signing in to the site.
Developer tools in the web browser revealed an access denied error on the URL http://sharepoint.domain.com/_api/contextinfo
The issue was resolved by disabling the “Require Use Remote Interfaces” setting on the web application as follows:
- In Central Admin \ Web Applications
- Select the web application
- Choose Authentication from the ribbon
- On each zone, remove the tick from “Require Use Remote Interfaces”
- Click OK
The double authentication prompt only occurred on specific activities e.g. editing pages.
In my case this problem occurred after extending a Web Application. In the primary web application I had customised the authentication settings (in IIS). These settings reverted back to defaults after I extended the web application via Central Admin.