Type interface {} is interface with no methods

I am using https://github.com/kataras/iris golang web framework. This is follow up mail from the last question asked here - Fetching Logged in User Info for display - Golang Template

I am finally using code that was mentioned in the previous post like:-

ctx.Values().Get("user")

and the value that user is set or has is "Struct" type:-

// users is struct below

var user users

// details are fetched from DB and assigned to user 
// like mentioned here http://go-database-sql.org/retrieving.html 
// Now value is set
ctx.Values().Set("user", user);

But after getting the value, When I use in different handler and print:-

user := ctx.Values().Get("user")
fmt.Println(user.ID)

I get the error:-

user.ID undefined (type interface {} is interface with no methods)

I need help in "Type assertion" for the interface. How can I "type assert" above value?