Temporary solution of authentication changes for Dart 2.15

[Swain]

You will failed in running pub get and pub publish when you use unpub as your private self-hosted pub server after upgrading Dart 2.15 because the changing.

We introduce the cli app named unpub_auth for the temporary solution.

• Pub: https://pub.dev/packages/unpub_auth
• source: https://github.com/bytedance/unpub/tree/master/unpub_auth

[Brett Sutton]

comment so this item is in my history