What are the implications of an incorrect `Host` header on CloudFront requests and potential 403 errors?

The `Host` header is crucial for CloudFront's origin behavior, especially when you have multiple origins or are using custom origins that rely on the `Host` header to route requests. If the `Host` header in the client's request does not match what CloudFront expects for the configured origin, or if the origin server itself rejects requests based on the `Host` header, it can lead to a 403 error. **Resolution:** - **Check Origin Configuration:** Ensure that your CloudFront origin settings correctly specify the `Origin Domain Name` and `Origin Protocol Policy`. - **Customize Origin Request:** If your origin requires a specific `Host` header, you can configure CloudFront to forward the `Host` header to the origin. In the CloudFront distribution settings, under 'Origin settings', you can choose 'Cache based on selected request parameters' and specifically include the `Host` header. Alternatively, you can use a Lambda@Edge function to modify the `Host` header before it's sent to the origin.