Creates, updates, or deletes an HMAC key.

Use a POST HMAC key request to:

- [Create an HMAC key](https://docs.cloud.google.com/storage/docs/xml-api/post-hmac-create.md.txt)
- [Update an HMAC key](https://docs.cloud.google.com/storage/docs/xml-api/post-hmac-update.md.txt)
- [Delete an HMAC key](https://docs.cloud.google.com/storage/docs/xml-api/post-hmac-delete.md.txt)

## Common request headers

The following are common request headers for POST HMAC Key.

| Header | Description | Required |
|---|---|---|
| `Authorization` | The authentication string for the request. | Yes |
| `Date` | The date and time of the request. | Yes |
| `Host` | The URI for Cloud Storage. For more information, see [Request Endpoints](https://docs.cloud.google.com/storage/docs/request-endpoints.md.txt). | Yes |
| `x-goog-user-project` | The project to be billed for charges associated with the request. | No |