     public func registerRoutes() {
         droplet.group("courses", ":id") { courses in
             courses.get("users", handler: users)
+            courses.post("users", handler: addUser)
         }
     }
 

        
        return try JSON(node: course.users().all().makeNode(context: UserSensitiveContext()))
    }

}

import Vapor
import Fluent
import HTTP

public final class CoursesController: ResourceRepresentable {
