How do I use GenerateEmailConfirmationTokenAsync in the context of Web API 2

I have tried it in a MVC 5 project and it works. I am now building a Web API 2 based app and need to send out emails to registered users to confirm their registration. I can't use the UserManager. Can anyone help, please?

public async Task<IdentityResult> RegisterUser(UserModel userModel) { IdentityUser user = new IdentityUser { UserName = userModel.UserName, Email = userModel.UserName }; IdentityResult result = await userManager.CreateAsync(user, userModel.Password); if (result.succeeded) { // Cannot use UserManager.GenerateEmailConfirmationTokenAsync(user.Id) // Send out email for confirmation } }