New Post: MVC Function with Identity Framework: No owin.Environment item was found in the context.

Quickly found the problem... MVC Functions are executed inside its own HttpContext, which is a copy of the main content which you can see here https://github.com/Orckestra/C1-Packages/blob/master/Composite.AspNet.MvcFunctions/Composite.AspNet.MvcFunctions/FunctionProvider/MvcFunctionBase.cs#L171.

And while they pretend to copy all the data from the Parent to the Child context, as you can see here https://github.com/Orckestra/C1-Packages/blob/master/Composite.AspNet.MvcFunctions/Composite.AspNet.MvcFunctions/FunctionProvider/MvcFunctionBase.cs#L156, they are not very good at it. IMO ie. ALL Items should be copied, which would have copied the OwinContext as well.

A quick fix for you is to resolve OwinContext on HttpContext.Current, instead of the HttpContext properties on Controller like this

protected IOwinContext OwinContext
{
   get { return System.Web.HttpContext.Current.GetOwinContext(); }
}

And then you can get your managers like this

public ApplicationSignInManager SignInManager
{
    get { return _signInManager ?? OwinContext.Get<ApplicationSignInManager>(); }
    private set { _signInManager = value; }
}

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