code: func NewSigner(policy *config.Signing) (*Signer, error) {
  	if policy != nil {
  		if !policy.Valid() {
  			return nil, cferr.New(cferr.PolicyError,
  				cferr.InvalidPolicy)
  		}
  		return &Signer{policy: policy}, nil
  	}
  
  	return nil, cferr.New(cferr.PolicyError,
  		cferr.InvalidPolicy)
  }
docs: // NewSigner creates a new remote Signer directly from a
  // signing policy.