A little helper function to generate the shared access token (SAS) to talk to e.g. Azure Notification Hubs

sas.go

package main

import (
	"crypto/hmac"
	"crypto/sha256"
	"encoding/base64"
	"fmt"
	"net/url"
	"strconv"
	"text/template"
	"time"
)

const day = time.Minute * 60 * 24

func main() {
	SaS := createSharedAccessToken("<ServiceBusURL>", "<PolicyName>", "<SecretKey>")
	fmt.Println(SaS)
}

// createSharedAccessToken generates the "Authorization" header value necessary to talk
// to Azure Notification Hubs. The parameter uri corresponds to the resource
// you send the request to. E.g.:
// 		https://mysite.servicebus.windows.net/mysite-notif/registrations/?api-version=2015-01
//
// You will get the other parameters from the notification hub access
// policies connection string. E.g:
// 		Endpoint=sb://long-url.servicebus.windows.net/;SharedAccessKeyName=ABC;SharedAccessKey=XYZ
func createSharedAccessToken(uri string, sharedAccessKeyName string, sharedAccessKey string) string {

	// expiry date is set to a time in the future. In the following example it is one day
	//   https://code.msdn.microsoft.com/Shared-Access-Signature-0a88adf8
	expiry := time.Now().Add(day).Unix()
	expiryStr := strconv.FormatInt(expiry, 10)

	// construct the string we need to sign with HMAC SHA256
	stringToSign := template.URLQueryEscaper(uri) + "\n" + expiryStr

	// Generate the signature of the above string
	hash := hmac.New(sha256.New, []byte(sharedAccessKey))
	hash.Write([]byte(stringToSign))
	signature := base64.StdEncoding.EncodeToString(hash.Sum(nil))

	q := url.Values{}
	q.Add("sr", uri)
	q.Add("sig", signature)
	q.Add("se", expiryStr)
	q.Add("skn", sharedAccessKeyName)

	// construct the shared access signature token
	return "SharedAccessSignature " + q.Encode()
}