Slack Source

When to use this source type

Choose the SLACK source type when Slack is the system sending webhook requests into FastHook. The source type keeps sender-specific setup close to the source: accepted methods, verification headers, challenge handling, and the exact credential fields are documented together so operators do not need to translate a generic HMAC form into a provider-specific contract.

FastHook verifies the source before accepted traffic is queued. A valid request is stored with verified: true, then connections route it to destinations. A bad signature, wrong token, or missing provider header is rejected as SOURCE_AUTH_FAILED. A method outside the allowed set is rejected as SOURCE_METHOD_NOT_ALLOWED.

FastHook configuration

In the dashboard, create a source, set Source Type to Slack, keep Authenticate enabled when verification is required, and fill the fields below.

{
  "type": "SLACK",
  "config": {
    "auth_type": "PROVIDER_SIGNATURE",
    "auth": {
      "provider": "SLACK",
      "webhook_signing_secret": "provider-secret"
    },
    "allowed_http_methods": ["POST","PUT","PATCH","DELETE"]
  }
}

curl -X POST "https://api.fasthook.io/v1/sources" \
  -H "Authorization: Bearer $FASTHOOK_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
  "name": "Slack production",
  "type": "SLACK",
  "config": {
    "auth_type": "PROVIDER_SIGNATURE",
    "auth": {
      "provider": "SLACK",
      "webhook_signing_secret": "provider-secret"
    },
    "allowed_http_methods": [
      "POST",
      "PUT",
      "PATCH",
      "DELETE"
    ]
  }
}'

URL verification before event callbacks

Some providers do not send normal event payloads first. They validate the callback URL or subscription contract before delivery starts, so keep the methods listed below enabled during setup.

1. Slack sends a signed url_verification payload to the Source URL.
2. FastHook verifies the Slack signature and returns the challenge string as plaintext.
3. After Slack accepts the challenge response, Events API callbacks continue as signed POST requests.

HTTP methods

This source accepts only the methods listed below. Keep the set narrow so provider mistakes and accidental test calls are visible as rejected requests instead of being silently accepted.

Special response: For Slack url_verification payloads, FastHook returns the challenge string as text.

Headers and verification

FastHook verifies the provider-specific values below before the request is accepted. The comparison is done against the raw inbound request body or the exact provider-specific signing input described here.

FastHook verifies x-slack-signature by signing v0:timestamp:raw-body and checks the timestamp tolerance.

Provider setup checklist

1. Create a Slack app and enable the Events API.
2. Paste the FastHook Source URL into Slack's Request URL field.
3. Use Slack's signing secret in the FastHook Webhook Signing Secret field.
4. Open Slack Events API documentation when you need the provider's event list, dashboard steps, or retry policy.

Supported event types and payload shape

FastHook stores the original Slack request before routing so filters, transformations, retries, and replay decisions can use the same provider evidence. Use stable headers and payload fields for routing rather than relying on receiver-side logs alone.

• Events API callbacks usually route by Slack event.type and team_id after URL verification succeeds.
• Keep inbound Slack event handling separate from outbound Slack notification destinations.

Troubleshooting

• No request appears: the provider is not calling the generated FastHook Source URL, the source URL was copied before saving, or the provider has not completed its setup validation.
• 405 method rejected: the provider sent a method outside POST, PUT, PATCH, DELETE. Edit the source only if the provider documentation says that method is expected.
• 401 source auth failed: check the configured FastHook field, the provider signing secret, and the header names listed on this page.
• Signature mismatch: make sure the provider signs the same public Source URL it calls and that no proxy, parser, or manual resend changed the raw request body before FastHook received it.

Slack source FAQ

Related docs

• Sources
• Source authentication
• Webhook signature validation
• Custom source responses
• Provider event routing