code: def validate_headers_for_server(credentials)
        client_customer_id = credentials[:client_customer_id]
  
        if client_customer_id and (!(client_customer_id.is_a?(Integer) or
            (client_customer_id =~ /^\d+(-\d+-\d+)?$/)))
          raise AdwordsApi::Errors::BadCredentialsError,
              'Invalid client customer ID: %s' % client_customer_id.to_s
        end
  
        token = credentials[:developer_token]
        if token.nil? || token.empty?
          raise AdwordsApi::Errors::BadCredentialsError,
              'Developer token is missing, check credentials.'
        end
        return nil
      end
docs: Validates that the right credentials are being used for the chosen
   environment.
  
   Raises:
   - AdwordsApi::Errors:BadCredentialsError if supplied credentials are not
   valid.