Authenticate Azure Event Grid clients using access keys or shared access signatures

This article provides information on authenticating clients that publish events to Azure Event Grid topics, domains, partner namespaces using access key or Shared Access Signature (SAS) token.

Access key authentication is the simplest form of authentication. You can pass the access key as an HTTP header or a URL query parameter.

Pass the access key as a value for the HTTP header: aeg-sas-key.

aeg-sas-key: XXXXXXXXXXXXXXXXXX0GXXX/nDT4hgdEj9DpBeRr38arnnm5OFg==

You can also specify aeg-sas-key as a query parameter.

https://<yourtopic>.<region>.eventgrid.azure.cn/api/events?aeg-sas-key=XXXXXXXX53249XX8XXXXX0GXXX/nDT4hgdEj9DpBeRr38arnnm5OFg==

For instructions on how to get access keys for a topic or domain, see Get access keys.

SAS tokens for an Event Grid resource include the resource, expiration time, and a signature. The format of the SAS token is: r={resource}&e={expiration}&s={signature}.

The resource is the path for the Event Grid topic to which you're sending events. For example, a valid resource path is: https://<yourtopic>.<region>.eventgrid.azure.cn/api/events. To see all the supported API versions, see Microsoft.EventGrid resource types.

First, programmatically generate a SAS token and then use the aeg-sas-token header or Authorization SharedAccessSignature header to authenticate with Event Grid.

The following C# and Python examples show you how to create a SAS token for use with Event Grid:

C# example

static string BuildSharedAccessSignature(string resource, DateTime expirationUtc, string key)
{
    const char Resource = 'r';
    const char Expiration = 'e';
    const char Signature = 's';

    string encodedResource = HttpUtility.UrlEncode(resource);
    var culture = CultureInfo.CreateSpecificCulture("en-US");
    var encodedExpirationUtc = HttpUtility.UrlEncode(expirationUtc.ToString(culture));

    string unsignedSas = $"{Resource}={encodedResource}&{Expiration}={encodedExpirationUtc}";
    using (var hmac = new HMACSHA256(Convert.FromBase64String(key)))
    {
        string signature = Convert.ToBase64String(hmac.ComputeHash(Encoding.UTF8.GetBytes(unsignedSas)));
        string encodedSignature = HttpUtility.UrlEncode(signature);
        string signedSas = $"{unsignedSas}&{Signature}={encodedSignature}";

        return signedSas;
    }
}

Python example

def generate_sas_token(uri, key, expiry=3600):
    ttl = datetime.datetime.utcnow() + datetime.timedelta(seconds=expiry)
    encoded_resource = urllib.parse.quote_plus(uri)
    encoded_expiration_utc = urllib.parse.quote_plus(ttl.isoformat())

    unsigned_sas = f'r={encoded_resource}&e={encoded_expiration_utc}'
    signature = b64encode(HMAC(b64decode(key), unsigned_sas.encode('utf-8'), sha256).digest())
    encoded_signature = urllib.parse.quote_plus(signature)
    
    token = f'r={encoded_resource}&e={encoded_expiration_utc}&s={encoded_signature}'

    return token

Here's an example that shows how to pass a SAS token as a value for the aeg-sas-token header.

aeg-sas-token: r=https%3a%2f%2fmytopic.eventgrid.azure.cn%2fapi%2fevents&e=6%2f15%2f2017+6%3a20%3a15+PM&s=XXXXXXXXXXXXX%2fBPjdDLOrc6THPy3tDcGHw1zP4OajQ%3d

This example shows how to pass a SAS token as a value for the Authorization header.

Authorization: SharedAccessSignature r=https%3a%2f%2fmytopic.eventgrid.azure.cn%2fapi%2fevents&e=6%2f15%2f2017+6%3a20%3a15+PM&s=XXXXXXXXXXXXX%2fBPjdDLOrc6THPy3tDcGHw1zP4OajQ%3d

• Send events to your custom topic.