# Google API Core Client - Class HeaderCredentialsInterface (1.43.0)

1.43.0 (latest) 1.42.5 1.40.0 1.38.2 1.36.1 1.35.1 Reference documentation and code samples for the Google API Core Client class HeaderCredentialsInterface.

Classes which implement this interface in this package:

- [ApiKeyHeaderCredentials](https://docs.cloud.google.com/php/docs/reference/gax/latest/ApiKeyHeaderCredentials)
- [CredentialsWrapper](https://docs.cloud.google.com/php/docs/reference/gax/latest/CredentialsWrapper)
- [InsecureCredentialsWrapper](https://docs.cloud.google.com/php/docs/reference/gax/latest/InsecureCredentialsWrapper)

## Namespace

Google \\ ApiCore

## Methods

### getAuthorizationHeaderCallback

| **Parameter** ||
|---|---|
| **Name** | **Description** |
| `audience` | `string|null` optional audience for self-signed JWTs. |

| **Returns** ||
|---|---|
| **Type** | **Description** |
| `callable|null` | Callable function that returns an authorization header. |

### checkUniverseDomain

Verify that the expected universe domain matches the universe domain from the credentials.