URL rewrite in OWIN middleware
I found a working solution.
Unfortunately, I needed to include System.Web. I'm directly altering the RouteData object in the RequestContext.
System.Web.Routing.RequestContext requestContext = context.Environment["System.Web.Routing.RequestContext"] as System.Web.Routing.RequestContext;
requestContext.HttpContext.RewritePath("Home/Global");
requestContext.RouteData.Values["action"] = "Global";
But this feels too hacky to my tastes... I'm not sure if this is the right solution so I won't accept this as the valid answer, maybe someone will come with a better solution.