Pavan@PAVAN-PC c:xampphtdocsmagedemo
# composer config repositories.data-migration-tool git https://github.com/magento/data-migration-tool

Pavan@PAVAN-PC c:xampphtdocsmagedemo
# composer require magento/data-migration-tool:2.2.6
./composer.json has been updated
Loading composer repositories with package information                                                                                             Authentication required (repo.magento.com):
      Username: fasfdsdafasfsdafasdf
      Password:

Installation failed, reverting ./composer.json to its original content.


  [ComposerDownloaderTransportException]
  Invalid credentials for 'https://repo.magento.com/packages.json', aborting.


require [--dev] [--prefer-source] [--prefer-dist] [--no-progress] [--no-update] [--no-scripts] [--update-no-dev] [--update-with-dependencies] [--ignore-platform-reqs] [--prefer-stable] [--prefer-lowest] [--sort-packages] [-o|--optimize-autoloader] [-a|--classmap-authoritative] [--] [<packages>]...