# Registrations

**NB**: If your client does not support add custom headers. Please contact us and we can manually enable the below features for your validators.

### Optional Authentication with the `x-api-key` Header

Users can obtain an api key from us and Authenticate via the `x-api-key` header. Validators registered with a valid authentication header will automatically skip any delay before `get_payload` is returned.

Example:

```
x-api-key: hcDL4sdCpIDgg6rvFkdUWdNc
```

### Customizing Validator Preferences with the `x-preferences` Header

Users can customize preferences for validators by including the `x-preferences` header with a JSON string of their settings.

Preferences include:

* `filtering:` A string indicating which filtering policy to use ("regional" or "global"). 
* `trusted_builders`: Specify a list of builders whose blocks are accepted. 
* `header_delay`: If set to false, will disable any relay-level delays for the `get_header` response.

Example:

```
x-preferences: {"filtering": "global", "trusted_builders": ["Titan", "Beaver", "Rsync"], "header_delay": false}
```

### Default Preferences

In the absence of the `x-preferences` header, the following defaults apply:

* **Filtering**: `"global"` (no filtering).
* **Header Delay**: `true` (relay-level `get_header` delays enabled).
* **Trusted Builders**: `no default` (if you do not want to enforce any Trusted Builder rules, omit this key).

Specifying a single preference (e.g., `{"header_delay": false}`) overrides only that setting, with others remaining at their default values.