Integrations

Linear Webhooks Custom Headers

Linear outgoing webhooks include Linear-specific headers such as Linear-Delivery, Linear-Event, and Linear-Signature. In Linear's webhook docs, those are the provider headers your receiver uses for delivery identity, event routing, and signature verification.

If your receiver also requires your own header such as Authorization, x-api-key, orx-linear-integration-secret, receive Linear in FastHook first. FastHook verifies Linear's Linear-Signature, stores the original request, and adds the custom header on the outgoing HTTP destination delivery.

Linear request accepted by FastHook and delivered to a receiver with destination authentication. — Keep Linear provider headers on ingress. Add receiver-specific custom headers on the FastHook destination.

Linear headers vs custom destination headers

Header	Where it applies	FastHook behavior
`Linear-Signature`	Linear to FastHook source	Verifies HMAC-SHA256 over the raw Linear webhook body.
`Linear-Delivery`	Linear to FastHook source	Captured with the request and useful for debugging and idempotency.
`Linear-Event`	Linear to FastHook source	Captured as provider context and useful for connection filters.
`CUSTOM_HEADER`	FastHook destination to your receiver	Sends your configured `config.auth.header_name` and `config.auth.value` with each routed delivery.

Create the Linear source

Create Linear source

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

Add an outgoing custom header

Use an HTTP destination with auth_type set to CUSTOM_HEADER when the downstream service expects a static secret header. This is the common workaround when a Linear webhook target needs an extra receiver credential.

Create HTTP destination with a custom header

curl -X POST "https://api.fasthook.io/v1/destinations" \
  -H "Authorization: Bearer $FASTHOOK_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "name": "linear-events-api",
    "type": "HTTP",
    "config": {
      "url": "https://api.example.com/webhooks/linear",
      "http_method": "POST",
      "auth_type": "CUSTOM_HEADER",
      "auth": {
        "header_name": "x-linear-integration-secret",
        "value": "receiver-shared-secret"
      },
      "rate_limit": 20,
      "rate_limit_period": "second"
    }
  }'

Route Linear events to that destination

Keep routing rules on the connection. A typical Linear setup routes issue changes, comments, projects, cycles, or SLA events to different downstream receivers while reusing the same verified Linear source.

Filter by the body type or action fields when event families need different receivers.
Use Linear-Delivery, webhookId, or Linear entity ids as idempotency inputs.
Use request replay after routing changes; use event retry when only one destination attempt failed.

Debug missing Linear custom headers

If Linear-Signature is missing, inspect the inbound request from Linear and confirm it reached the FastHook Source URL.
If your receiver's secret header is missing, check the HTTP destination auth_type and config.auth.header_name.
If Linear signature verification fails, keep the raw body unchanged and confirm the webhook signing secret.
If the destination returns 401 or 403, inspect the FastHook attempt body and response headers before retrying or replaying.