VTex Generate authentication token

Generate a [token](https://developers.vtex.com/vtex-rest-api/docs/getting-started-authentication#user-token) from a given [app key and app token](https://help.vtex.com/en/tutorial/application-keys--2iffYzlvvz4BDMr6WGUtet) pair. You can use this token to authenticate requests to VTEX APIs by sending it as a header named `VtexIdclientAutCookie`. The token's permissions are the same as [defined to the credential pair](https://help.vtex.com/en/tutorial/application-keys--2iffYzlvvz4BDMr6WGUtet#man...