You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: routing.go
    path of file: ./repos/highlight/backend/routing
    
    the code of the file until where you have to start completion: package routing

import (
	"context"
	"net/url"

	log "github.com/sirupsen/logrus"
)

type Referrer string

const (
	Discord        Referrer = "discord"
	Email          Referrer = "email"
	Slack          Referrer = "slack"
	Webhook        Referrer = "webhook"
	MicrosoftTeams Referrer = 
    
func AttachQueryParam(ctx context.Context, u string, key string, value string) string {
	url, err := url.Parse(u)
	if err != nil {
		log.WithContext(ctx).Errorf("Failed to parse url: %s", u)
		log.WithContext(ctx).Error(err)
		return u
	}

	values := url.Query()
	values.Add(key, value)
	url.RawQuery = values.Encode()

	return url.String()
}