This method should return an implementation of `\League\OAuth2\Server\Entities\RefreshTokenEntityInterface`. You can use the following traits to help you implement the required methods from that interface:
*`getAccessToken()->getIdentifier() : string` the linked access token's identifier.
JWT access tokens contain an expiry date and so will be rejected automatically when used. You can safely clean up expired access tokens from your database.
## revokeRefreshToken() : void
This method is called when a refresh token is used to reissue an access token. The original refresh token is revoked a new refresh token is issued.
This method is called when an refresh token is used to issue a new access token. Return `true` if the refresh token has been manually revoked before it expired. If the token is still valid return `false`.