Can't get UserManager from OwinContext in apicontroller

I'm following a Microsoft sample to implement email validation with Identity 2.0.0

I'm stuck at this part

public ApplicationUserManager UserManager
{
   get
   {
      return _userManager ?? HttpContext.GetOwinContext().GetUserManager<ApplicationUserManager>();
   }
   private set
   {
      _userManager = value;
   }
}

This works in an controller but HttpContext doesn't contain any GetOwinContext method in an ApiController.

So I tried HttpContext.Current.GetOwinContext() but the method GetUserManager doesn't exist.

I can't figure out a way to get the UserManager I build in Startup.Auth.cs

// For more information on configuring authentication, please visit http://go.microsoft.com/fwlink/?LinkId=301864
public void ConfigureAuth(IAppBuilder app)
{
    //Configure the db context, user manager and role manager to use a single instance per request
    app.CreatePerOwinContext(ApplicationDbContext.Create);
    app.CreatePerOwinContext<ApplicationUserManager>(ApplicationUserManager.Create); 
    ...
}

this line

app.CreatePerOwinContext<ApplicationUserManager>(ApplicationUserManager.Create);

calls the following function to configure the UserManager

public static ApplicationUserManager Create(IdentityFactoryOptions<ApplicationUserManager> options, IOwinContext context)
{
     var manager = new ApplicationUserManager(new UserStore<ApplicationUser>(context.Get<ApplicationDbContext>()));
     //Configure validation logic for usernames
     manager.UserValidator = new UserValidator<ApplicationUser>(manager)
     {
         AllowOnlyAlphanumericUserNames = false,
         RequireUniqueEmail = true
     };

     // Configure user lockout defaults
     manager.UserLockoutEnabledByDefault = true;
     manager.DefaultAccountLockoutTimeSpan = TimeSpan.FromMinutes(5);
     manager.MaxFailedAccessAttemptsBeforeLockout = 5;

     manager.EmailService = new EmailService();

     var dataProtectionProvider = options.DataProtectionProvider;
     if (dataProtectionProvider != null)
     {
         manager.UserTokenProvider = new DataProtectorTokenProvider<ApplicationUser>(dataProtectionProvider.Create("ASP.NET Identity"));
     }
     return manager;
}

How can I access this UserManager in an ApiController?

I really misunderstood your question earlier. You are just missing some using statements, I think.

The GetOwinContext().GetUserManager<ApplicationUserManager>() is in Microsoft.AspNet.Identity.Owin.

So try add this part:

using Microsoft.AspNet.Identity.Owin;
using Microsoft.AspNet.Identity; // Maybe this one too

var manager = HttpContext.Current.GetOwinContext().GetUserManager<UserManager<User>>();

This extension method may be a better solution if you want to unit test your controllers.

using System;
using System.Net.Http;
using System.Web;
using Microsoft.Owin;

public static IOwinContext GetOwinContext(this HttpRequestMessage request)
{
    var context = request.Properties["MS_HttpContext"] as HttpContextWrapper;
    if (context != null)
    {
        return HttpContextBaseExtensions.GetOwinContext(context.Request);
    }
    return null;
}

Usage:

public ApplicationUserManager UserManager
{
   get
   {
      return _userManager ?? Request.GetOwinContext().GetUserManager<ApplicationUserManager>();
   }
   private set
   {
      _userManager = value;
   }
}

This single line of code saved my day...

       var manager = 
       new ApplicationUserManager(new UserStore<ApplicationUser>(new ApplicationDbContext()));

You can use it within a controller action to get an instance of UserManager.