> For the complete documentation index, see [llms.txt](https://docs.tonomy.io/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.tonomy.io/run-tonomy-gov-os/reference/api.md).

# Application Interface (API)

The API is used by integration applications to do interact with Tonomy ID, such as using the single sign-on (SSO) flow and signing data.

* [ExternalUser class reference](https://unpkg.com/@tonomy/tonomy-id-sdk/build/sdk/types/api/externalUser.d.ts)

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