> For the complete documentation index, see [llms.txt](https://api.circle.so/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://api.circle.so/apis/headless/auth-sdk.md).

# Auth SDK

<figure><img src="https://3386231300-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FTxViy1AlkVpH99B9E7eY%2Fuploads%2FH1RKAOKwlA00zyTFDgJy%2FHeadless%20Auth%20SDK.jpg?alt=media&amp;token=1dca788e-8401-4cae-9686-0b36cb82197a" alt=""><figcaption></figcaption></figure>

{% hint style="info" %}
**The Headless Auth SDK is intended to be used only with server-side apps to authenticate your website/app with your secure App Token. This token should be kept secret, and should not be made available to anyone on the client side for security reasons.**
{% endhint %}