> For the complete documentation index, see [llms.txt](https://docs.atsign.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.atsign.com/dart-sdk/authentication.md).

# Authentication

- [Onboarding a new Atsign](https://docs.atsign.com/dart-sdk/authentication/onboarding-a-new-atsign.md): Learn how to do the initial onboard for an Atsign in your Dart application using AtAuth.onboard
- [Authenticating an existing Atsign](https://docs.atsign.com/dart-sdk/authentication/authenticating-an-existing-atsign.md): Learn how to do the initial onboard for an Atsign in your Dart application using AtAuth.authenticate
- [Create an AtClient instance](https://docs.atsign.com/dart-sdk/authentication/create-an-atclient-instance.md): The goal of authentication is to create a ready-to-use AtClient instance.