server.go
func (ctx *RequestCtx) SetUserValue(key string, value interface{}) {
	ctx.userValues.Set(key, value)
}
func (ctx *RequestCtx) SetUserValue(key string, value interface{}) {
	ctx.userValues.Set(key, value)
}
// SetUserValue stores the given value (arbitrary object)
// under the given key in ctx.
//
// The value stored in ctx may be obtained by UserValue*.
//
// This functionality may be useful for passing arbitrary values between
// functions involved in request processing.
//
// All the values are removed from ctx after returning from the top
// RequestHandler. Additionally, Close method is called on each value
// implementing io.Closer before removing the value from ctx.