docs: def __get_auth(self):
          '''Return auth headers. Will use API Keys if present in settings.'''
          if self.api_key == None and self.login == None:
              self.logger.error("No authentication provided! Unable to connect.")
              sys.exit(1)
  
          if self.api_key == None:
              self.logger.info("Authenticating with email/password.")
              return [
                  "email: " + self.login,
                  "password: " + self.password
              ]
          else:
              self.logger.info("Authenticating with API Key.")
              # To auth to the WS using an API key, we generate a signature of a nonce and
              # the WS API endpoint.
              nonce = generate_nonce()
              return [
                  "api-nonce: " + str(nonce),
                  "api-signature: " + generate_signature(self.api_secret, 'GET', '/realtime', nonce, ''),
                  "api-key:" + self.api_key
              ]