func (s *UserService) Authorized(handle, method, rawurl string) bool {
	s.lock.Lock()
	fmt.Fprintln(s.writer, handle)
	fmt.Fprintln(s.writer, method)
	fmt.Fprintln(s.writer, rawurl)
	s.lock.Unlock()
	return true
}
Authorized implements the multipass.UserService.Authorized method. It writes
the given arguments to the UserService's writer element followed by a
newline character.
package io
import (
	"fmt"
	"io"
	"sync"
)
type UserService struct {
	writer io.Writer
	lock   sync.Mutex
}
func NewUserService(w io.Writer) *UserService {
	return &UserService{
		writer: w,
	}
}
func (s *UserService) Listed(handle string) bool {
	s.lock.Lock()
	fmt.Fprintln(s.writer, handle)
	s.lock.Unlock()
	return len(handle) > 0
}