# ApiKey

Learn how to provide the API key that authenticates your application.

This class represents the API key that authenticates your application with Croct. It optionally carries a private key used to sign user tokens when you [identify](/reference/sdk/php/api/core/plug/identify) visitors.

Provide it, or its serialized string, [when you create the SDK](/reference/sdk/php/api/core/croct/plug).

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Use the summary below to quickly jump to a specific topic:

- [parse](/reference/sdk/php/api/authentication/api-key/parse): Learn how to create an API key from its serialized string.
- [of](/reference/sdk/php/api/authentication/api-key/of): Learn how to create an API key from an identifier and a private key.
- [getIdentifier](/reference/sdk/php/api/authentication/api-key/get-identifier): Learn how to get the public identifier of the API key.
- [hasPrivateKey](/reference/sdk/php/api/authentication/api-key/has-private-key): Learn how to check whether the API key can sign user tokens.