Using ClickHouse as a webhook endpoint with HMAC verification

One of my favorite features of ClickHouse 25.12 was the HMAC function for message authentication using a shared key.

ClickHouse has always been able to act as a webhook endpoint, but with the HMAC function we can now verify webhook requests, filtering out those that didn't come from the expected source. We'll start by seeing how this works with a local example, before moving onto a real-life example using ClickHouse Cloud as a GitHub webhook endpoint.

The webhook pattern #

One cool thing about ClickHouse is the ability to chain tables together using materialized views. Data gets ingested into one table, a materialized view acts as a SQL trigger, and the results are written to another table.

This becomes especially powerful when combined with the Null table engine. Rather than storing data, the Null table engine forwards everything it receives to any connected materialized views — making it the perfect staging layer.

The result is a clean three-step pattern:

1. A staging table receives all incoming data
2. A materialized view validates and transforms it
3. A final table stores only the verified data

Create the tables #

Let's have a look at how to set this all up in ClickHouse. If you want to follow along, you'll need to have a ClickHouse server or ClickHouse Cloud service running.

First, let's create the staging table:

1CREATE TABLE webhook_staging (
2    received_at DateTime DEFAULT now(),
3    raw_payload String,
4    signature String DEFAULT getClientHTTPHeader('X-Hub-Signature-256')
5) ENGINE = MergeTree()
6ORDER BY received_at
7SETTINGS allow_get_client_http_header=1;

The allow_get_client_http_header setting is required because reading client headers is disabled by default.

We're creating the webhook_staging table with the MergeTree engine, so that we can debug incoming requests. In a production system we would use the Null engine and might also have a second materialized view that captures invalid requests.

Next, we have a table that's going to store only verified rows:

1CREATE TABLE webhook_logs (
2    received_at DateTime,
3    payload JSON
4) ENGINE = MergeTree()
5ORDER BY received_at;

And finally, we have a materialized view that validates the data:

1CREATE MATERIALIZED VIEW webhook_validator TO webhook_logs AS
2SELECT
3    received_at,
4    raw_payload::JSON as payload
5FROM webhook_staging
6WHERE signature = 'sha256=' || lower(hex(HMAC('SHA256', raw_payload, 'my_secret_key')));

We're comparing the signature from the request header to the expected signature computed using the shared secret key. Our shared secret key is my_secret_key.

If the incoming row doesn't match the expected signature, it won't be written to the webhook_logs table.

Create a restricted user #

When experimenting on our own machine, we could use the default admin user, but for a production system it's safer to create a dedicated user with minimal permissions. The user that we create will be used in the webhook URL that we construct later.

First, let's create the user:

1CREATE USER webhook_receiver
2IDENTIFIED WITH sha256_hash
3BY 'e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855';

The hash is the SHA256 of an empty string, so no password is needed when we construct the webhook URL.

Next, let's grant the user the permissions it needs:

1GRANT INSERT ON default.webhook_staging TO webhook_receiver;
2GRANT SELECT ON default.webhook_staging TO webhook_receiver;
3GRANT SHOW TABLES ON default.webhook_staging TO webhook_receiver;
4GRANT SHOW DATABASES ON default.* TO webhook_receiver;

If we want to be extra cautious, we could also apply rate limits to this user to guard against abuse.

Construct the webhook URL #

ClickHouse accepts inserts over HTTP, which means the whole webhook endpoint is a URL with the INSERT query embedded:

http://localhost:8123/?user=webhook_receiver&query=INSERT+INTO+webhook_staging+(raw_payload)+FORMAT+RawBLOB

The key parts:

• user=webhook_receiver -the restricted user we created
• query=INSERT INTO webhook_staging (raw_payload) FORMAT RawBLOB -the URL-encoded query that inserts the raw request body

FORMAT RawBLOB tells ClickHouse to treat the entire request body as a single string value rather than trying to parse it.

We can then test it out by sending a valid request i.e. one where the signature is computed with the correct key:

1PAYLOAD='{"event":"user_login","user_id":456}'
2SIGNATURE=$(echo -n ",[object Object]," | openssl dgst -sha256 -hmac "my_secret_key" | cut -d' ' -f2)
3
4curl -X POST "http://localhost:8123/?user=webhook_receiver&allow_get_client_http_header=1&query=INSERT%20INTO%20webhook_staging%20(raw_payload)%20FORMAT%20RawBLOB" \
5  -H "X-Hub-Signature-256: sha256=,[object Object]," \
6  -d ",[object Object],"

Let's now connect to our ClickHouse Server using ClickHouse Client:

1clienthouse client

And we can return the contents of webhook_staging and webhook_logs:

1SELECT * FROM webhook_staging;

Row 1:
──────
received_at: 2026-02-20 15:42:22
raw_payload: {"event":"user_login","user_id":456}
signature:   sha256=5a23c796b6248c725a6ec7fc2cf0788117d69d376ee6241f411a8887297d3ca4

1 row in set. Elapsed: 0.001 sec.

1SELECT * FROM webhook_logs;

Row 1:
──────
received_at: 2026-02-20 15:42:22
payload:     {
    "event": "user_login",
    "user_id": 456
}

1 row in set. Elapsed: 0.003 sec.

Both tables have the data. Now how about we send a request where we've computed the signature with a different key:

1PAYLOAD='{"event":"user_login","user_id":456}'
2SIGNATURE=$(echo -n ",[object Object]," | openssl dgst -sha256 -hmac "rogue_key" | cut -d' ' -f2)
3
4curl -X POST "http://localhost:8123/?user=webhook_receiver&allow_get_client_http_header=1&query=INSERT%20INTO%20webhook_staging%20(raw_payload)%20FORMAT%20RawBLOB" \
5  -H "X-Hub-Signature-256: sha256=,[object Object]," \
6  -d ",[object Object],"

Let's run our queries against webhook_staging:

Row 1:
──────
received_at: 2026-02-20 15:43:21
raw_payload: {"event":"user_login","user_id":456}
signature:   sha256=01f65041f2505f2b245f3caff410913a22a0ff8c7e8414c9fe1e861359973a7a

Row 2:
──────
received_at: 2026-02-20 15:42:22
raw_payload: {"event":"user_login","user_id":456}
signature:   sha256=5a23c796b6248c725a6ec7fc2cf0788117d69d376ee6241f411a8887297d3ca4

2 rows in set. Elapsed: 0.002 sec.

And now, webhook_logs:

Row 1:
──────
received_at: 2026-02-20 15:42:22
payload:     {
    "event": "user_login",
    "user_id": 456
}

1 row in set. Elapsed: 0.004 sec.

webhook_staging gets a new row, webhook_logs doesn't - the signatures didn't match so the materialized view dropped it.

GitHub webhook #

With the pattern established locally, let's wire it up to a real GitHub repository using ClickHouse Cloud. The structure is almost identical, with just one difference - the staging table picks up an extra event_type column (from the X-GitHub-Event header GitHub sends) and webhook_logs picks an event_type column as well.

The queries below create our tables and materialized view.

1CREATE TABLE webhook_staging (
2    received_at DateTime DEFAULT now(),
3    raw_payload String,
4    event_type String DEFAULT getClientHTTPHeader('X-GitHub-Event'),
5    signature String DEFAULT getClientHTTPHeader('X-Hub-Signature-256')
6) ENGINE = MergeTree()
7ORDER BY received_at
8SETTINGS allow_get_client_http_header=1;

1CREATE TABLE webhook_logs (
2    received_at DateTime,
3    event_type String,
4    payload JSON
5) ENGINE = MergeTree()
6ORDER BY received_at;

1CREATE MATERIALIZED VIEW webhook_validator TO webhook_logs AS
2SELECT
3    received_at,
4    event_type,
5    raw_payload::JSON as payload
6FROM webhook_staging
7WHERE signature = 'sha256=' || lower(hex(HMAC('SHA256', raw_payload, 'my_secret_key')));

In ClickHouse Cloud, click Connect to get your cluster URL, then build the webhook URL the same way - just swap localhost:8123 for your Cloud host and add allow_get_client_http_header=1:

https://<host>:8443/?user=webhook_receiver&allow_get_client_http_header=1&query=INSERT+INTO+webhook_staging+(raw_payload)+FORMAT+RawBLOB

Configure the GitHub webhook #

In your GitHub repository, go to Settings → Webhooks → Add webhook:

1. Paste your ClickHouse URL into Payload URL
2. Set Content type to application/json
3. Enter your secret key in the Secret field -this must match my_secret_key from the materialized view
4. Choose which events to send (push events are fine to start)
5. Click Add webhook

GitHub will immediately send a ping event. Refresh the webhook page and you should see "Last delivery was successful".

Verify it's working #

We can then explore the contents of each table by clicking their name.

You should see the ping event in both, which confirms the HMAC validation passed. Now make a change to your repository -commit to a branch, open a PR, merge it -and push events will appear in both tables.

Testing signature validation #

To confirm the validation is working, go back to GitHub, change the webhook secret to something different, then make another commit.

webhook_staging will have the new rows but webhook_logs won't - the materialized view computed a different HMAC and filtered them out.