How to Publish MQTT Messages via HTTP with Azure Event Grid (preview)

2025-08-07

Azure Event Grid now supports publishing MQTT messages via HTTP, enabling backend systems to send messages to devices without maintaining persistent MQTT connections. This approach simplifies integration for applications that prefer stateless communication, uses secure authentication with Entra ID, and provides scalable, reliable delivery to MQTT clients. In this article, you learn how to use the HTTP Publish API, obtain the necessary credentials, and verify message delivery using popular tools like Bruno, and MQTTX.

Note

This feature is currently in preview.

This article explains how to publish MQTT messages via HTTP with Azure Event Grid.

Get your connection details

Namespace fully qualified domain name (FQDN). Example: contoso.westus3-1.ts.eventgrid.azure.net.
Topic. Example: devices/CXa-23112/prompt.
Entra ID client credentials.

Get a bearer token

Run the following Azure CLI command to get a bearer token.

az account get-access-token --resource=https://<namespaceFQDN> --query accessToken -o tsv

Save this token to use in the Authorization: Bearer <TOKEN> header.

Here’s an example cURL command to simulate the HTTP Publish.

curl -X POST "https://contoso.westus3-1.ts.eventgrid.azure.net/mqtt/messages?topic=devices%2XXXX-0000%2Fprompt&api-version=2025-08-01-preview" \ 
  -H "Authorization: Bearer <ENTRA_TOKEN_HERE>" \ 
  -H "mqtt-qos: 1" \ 
  -H "mqtt-retain: 0" \ 
  -H "mqtt-response-topic: devices%2XXXX-00000%2Freply" \ 
  -H "mqtt-correlation-data: XXXXXXX" \ 
  -H "mqtt-user-properties: XXXXXXXXXXXX" \ 
  -H "Content-Type: text/plain;charset=UTF-8" \ 
  --data-raw "Please accept terms of licensing and agreement"

In this sample command:

Topic is percent-encoded.
Add optional headers for QoS, retain flag, response topic, user properties.
Payload goes in the request body.

Import to Bruno

Open Bruno.

Select Import Collection, and then select EventGrid_HTTP_Publish_Postman_Collection.json. Here's the content for the JSON file:

{
  "info": {
    "name": "Event Grid MQTT Broker - HTTP Publish",
    "schema": "https://schema.getpostman.com/json/collection/v2.1.0/collection.json"
  },
  "item": [
    {
      "name": "HTTP Publish to MQTT Broker",
      "request": {
        "method": "POST",
        "header": [
          {
            "key": "Authorization",
            "value": "Bearer {{entra_token}}"
          },
          {
            "key": "mqtt-qos",
            "value": "1"
          },
          {
            "key": "mqtt-retain",
            "value": "0"
          },
          {
            "key": "mqtt-response-topic",
            "value": "devices%2FCXa-23112%2Freply"
          },
          {
            "key": "mqtt-correlation-data",
            "value": "PlXCscK2wrbCuy8="
          },
          {
            "key": "mqtt-user-properties",
            "value": "[{\"Urgency\":\"alert\"},{\"RequestId\":\"55f4a7ee-b0b4-4d7f-8eb5-2edba2ced5d7\"}]"
          },
          {
            "key": "Content-Type",
            "value": "text/plain;charset=UTF-8"
          }
        ],
        "url": {
          "raw": "https://{{namespace}}/mqtt/messages?topic={{topic}}&api-version=2025-08-01-preview",
          "host": [
            "{{namespace}}"
          ],
          "path": [
            "mqtt",
            "messages"
          ],
          "query": [
            {
              "key": "topic",
              "value": "{{topic}}"
            },
            {
              "key": "api-version",
              "value": "2025-02-15-preview"
            }
          ]
        },
        "body": {
          "mode": "raw",
          "raw": "Please accept terms of licensing and agreement"
        }
      }
    }
  ],
  "variable": [
    {
      "key": "namespace",
      "value": "contoso.westus3-1.ts.eventgrid.azure.net"
    },
    {
      "key": "topic",
      "value": "devices/CXa-23112/prompt"
    },
    {
      "key": "entra_token",
      "value": "<ENTRA_TOKEN_HERE>"
    }
  ]
}

Go to Variables tab:
- Replace {{namespace}} with your namespace FQDN.
- Replace {{topic}} with your MQTT topic.
- Replace {{entra_token}} with your token from Step 2.
Select Send. You should get 202 or 204.

Verify in MQTTX

Use MQTTX or any MQTT library (like paho-mqtt Python) to subscribe to the same topic to confirm delivery.

Create a new connection in MQTTX:
- Host: contoso.westus3-1.ts.eventgrid.azure.net
- Port: 8883 (TLS)
- Client ID: same as your Entra Object ID
- Username/Password: N/A — use certificate or token auth if configured
Subscribe to the topic you used in the HTTP POST command.
Run the HTTP Publish and watch for the message in MQTTX. You should see your payload appear.

If the publish succeeds, you see:

HTTP Response: 204 No Content or 202 Accepted (depending on routing rules).
MQTT client sees the message instantly.

Troubleshoot

401 Unauthorized? — If the token is missing or expired: You get 401 Unauthorized. Refresh your token.
403 Forbidden? — If the topic is invalid or you don’t have rights: 403 Forbidden. Check your topic or permissions.
500 Internal Server Error - If routing fails internally, check metrics and diagnostic Logs for your Event Grid namespace.
Message doesn’t appear? — Ensure topic is percent-encoded in the URL, check broker routing config, and verify you’re using the same namespace.

For an overview of this feature, see HTTP Publish of MQTT messages with Azure Event Grid.

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How to Publish MQTT Messages via HTTP with Azure Event Grid (preview)

Get your connection details

Get a bearer token

Publish messages using HTTP

Verify in MQTTX

Troubleshoot

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