U4-8850 Configuring a custom BackOfficeUserManager type will not work if the type is not specifically BackOfficeUserManager

src/Umbraco.Core/Security/BackOfficeSignInManager.cs

@@ -17,7 +17,7 @@ namespace Umbraco.Core.Security
         private readonly ILogger _logger;
         private readonly IOwinRequest _request;
 
-        public BackOfficeSignInManager(BackOfficeUserManager userManager, IAuthenticationManager authenticationManager, ILogger logger, IOwinRequest request)
+        public BackOfficeSignInManager(UserManager<BackOfficeIdentityUser, int> userManager, IAuthenticationManager authenticationManager, ILogger logger, IOwinRequest request)
             : base(userManager, authenticationManager)
         {
             if (logger == null) throw new ArgumentNullException("logger");
@@ -35,7 +35,7 @@ namespace Umbraco.Core.Security
         public static BackOfficeSignInManager Create(IdentityFactoryOptions<BackOfficeSignInManager> options, IOwinContext context, ILogger logger)
         {
             return new BackOfficeSignInManager(
-                context.GetUserManager<BackOfficeUserManager>(), 
+                context.GetBackOfficeUserManager(), 
                 context.Authentication,
                 logger,
                 context.Request);