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Headers

Events includes two headers to help verify the authenticity of the payload.

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magic-hour-event-signature

A signatured created with the webhook secret key and a signed_payload, using HMAC with SHA-256

magic-hour-event-signature: d1747eb9491aadeac6173f1c9fd5f4aff87c8981ac53d87b0830199221ff50af

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magic-hour-event-timestamp

Time in seconds since the epoch. Use this value to check whether the request is within a reasonable window of the current time. Usually less than 5 minutes.

magic-hour-event-timestamp: 1729314984
HTTP headers are case insensitive

Using the header to verify the request ensures that the request is authentic. However, the header verification is not required to receive webhook events.

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Compute the signature

To verify the request, generate the signature in your application and confirm that it matches the request.

1

Create signed payload

Create a signed_payload by concatenating:

  • the timestamp as a string
  • the character .
  • the payload JSON (stringified)

For example,

1729314984.{"type":"video.started","object":{"id":"cuid","name":"Video","status":"rendering","type":"TEXT_TO_VIDEO","created_at":"2024-10-19T05:16:19.027Z","width":720,"height":1280,"total_frame_cost":300,"start_seconds":0,"end_seconds":5,"fps":30,"download":null}}
2

Compute the signature

Compute an HMAC with the SHA256 Hash function. Using the webhook secret as the key, and use the signed_payload as the message.

import hmac
import hashlib
import os

webhook_secret = os.getenv("MAGIC_HOUR_WEBHOOK_SECRET")

def compute_signature(signed_payload: str) -> str:
    return hmac.new(
        webhook_secret,
        payload,
        hashlib.sha256
    ).hexdigest()
3

Compare against request header

Compare the computed signature value against the header value and ensure they are identical. And verify that the timestamp is within a reasonable window.

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Integrate with handler

from fastapi import FastAPI, Request, HTTPException
import json

app = FastAPI()

@app.post("/webhook")
async def webhook(request: Request):
    # Get signature and timestamp from headers
    signature = request.headers.get('magic-hour-event-signature')
    timestamp = request.headers.get('magic-hour-event-timestamp')
    event = await request.json()

    # Verify timestamp is recent (within 5 minutes)
    if abs(int(time.time()) - int(timestamp) > 300
        raise HTTPException(status_code=401, detail="Timestamp too old")

    # Create signed payload and verify signature
    signed_payload = f"{timestamp}.{json.dumps(event.payload)}"
    if signature != compute_signature(signature):
        raise HTTPException(status_code=401, detail="Invalid signature")
    # rest of webhook logic

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