Remove Users from group in SharePoint 2013 from Client Object model.

This is the method that we use to remove users from groups in Sharepoint 2013

It's a bit more convoluted than it needs to be as for some reason Sharepoint 2013 appends the claim provider to the username, which means that rather than having:

 dev\duser1  

we have something like:

i:0#.w|dev\duser1  

so in order to ensure that the it will always find the relevant user, we do the extra call to ResolvePrincipal.

using Microsoft.SharePoint.Client;
using Microsoft.SharePoint.Client.Utilities;

     public bool RemoveUser(string url, string groupName, string userName)  
     {  
       using (ClientContext context = new ClientContext(url))  
       {  
         var principal = Utility.ResolvePrincipal(context, context.Web, userName, PrincipalType.User,  
           PrincipalSource.All, context.Web.SiteUsers, false);  
         context.ExecuteQuery();  
         if (principal.Value != null)  
         {  
           string login = principal.Value.LoginName;  
           GroupCollection siteGroups = context.Web.SiteGroups;  
           Group group = siteGroups.GetByName(groupName);  
           var query = context.LoadQuery(group.Users.Where(usr => usr.LoginName == login).Include(u => u.LoginName));  
           context.ExecuteQuery();  
           User user = query.SingleOrDefault();  
           if (user != null)  
           {  
             group.Users.RemoveByLoginName(user.LoginName);  
             context.ExecuteQuery();  
           }
           return true;               
         }  
       }  
       return false;  
     }