docs: def create_user(self, user_id,
                      roles=None, netmask=None,
                      secret=None, pubkey=None):
          u"""Create user for the Merchant given in the X-Mcash-Merchant header.
  
          Arguments:
              user_id:
                  Identifier for the user
              roles:
                  Role
              netmask:
                  Limit user connections by netmask, for example 192.168.1.0/24
              secret:
                  Secret used when authenticating with mCASH
              pubkey:
                  RSA key used for authenticating by signing
          """
          arguments = {'id': user_id,
                       'roles': roles,
                       'netmask': netmask,
                       'secret': secret,
                       'pubkey': pubkey}
          return self.do_req('POST', self.merchant_api_base_url + '/user/', arguments).json()