code: func Current(c *context.Context) *User {
  	v := c.Values.Get(userKey)
  	if v == nil {
  		return nil
  	}
  
  	u, ok := v.(*User)
  	if !ok {
  		return nil
  	}
  
  	return u
  }
docs: // Current returns the currently logged-in user, or nil if the user is not
  // signed in.