Hi, You have to add the configuration for the social network in UmbracoIdentityStartup.cs class. You will see there something like this:

namespace MyApp.Web.App_Start
{
    /// <summary>
    /// OWIN Startup class for UmbracoIdentity 
    /// </summary>
    public class UmbracoIdentityStartup : UmbracoDefaultOwinStartup
    {
        /// <summary>
        /// Configures services to be created in the OWIN context (CreatePerOwinContext)
        /// </summary>
        /// <param name="app"/>
        protected override void ConfigureServices(IAppBuilder app)
        {
            base.ConfigureServices(app);

            //Single method to configure the Identity user manager for use with Umbraco
            app.ConfigureUserManagerForUmbracoMembers<UmbracoApplicationMember>();

            //Single method to configure the Identity user manager for use with Umbraco
            app.ConfigureRoleManagerForUmbracoMembers<UmbracoApplicationRole>();
        }

        /// <summary>
        /// Configures middleware to be used (i.e. app.Use...)
        /// </summary>
        /// <param name="app"/>
        protected override void ConfigureMiddleware(IAppBuilder app)
        {
           ..............
            // Uncomment the following lines to enable logging in with third party login providers

            app.UseExternalSignInCookie(DefaultAuthenticationTypes.ExternalCookie);

            //app.UseMicrosoftAccountAuthentication(
            //  clientId: "",
            //  clientSecret: "");

            //app.UseTwitterAuthentication(
            //  consumerKey: "",
            //  consumerSecret: "");

            //app.UseFacebookAuthentication(
            //  appId: "",
            //  appSecret: "");            

            //app.UseGoogleAuthentication(
            //  clientId: "",
            //  clientSecret: "");

            //Lasty we need to ensure that the preview Middleware is registered, this must come after
            // all of the authentication middleware:
            app.UseUmbracoPreviewAuthentication(ApplicationContext, PipelineStage.Authorize);
        }
    }
}

If you need facebook login then you need to uncomment //app.UseFacebookAuthentication( // appId: "", // appSecret: "");
and set your appId and appSecret which you can get from https://developers.facebook.com/ In order to make this working you have to add referance to using Microsoft.Owin.Security.Facebook in your VS project

Regards Mila