Instanciate a AcmeClient using a private key for signing
Param: signingKey - The signingKey is the Acme account private key used to sign requests to the acme CA, in pem format.
an instance of AcmeException on fatal or unexpected errors.
See Implementation
Instanciate a AcmeClient using a private key for signing
Param: signingKey - The signingKey is the Acme account private key used to sign requests to the acme CA, in pem format.