> For the complete documentation index, see [llms.txt](https://devcenter.unico.io/unico-idpay/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://devcenter.unico.io/unico-idpay/en/integration/authentication.md).

# Authentication

To use IDPay, it is necessary to authenticate via access token, using the OAuth2 authentication system.

Unico's OAuth2 authentication system supports server-to-server interaction between a web application and Unico's services.

For this scenario, you will need a service account, which is a non-personal account that belongs to your application and not to an individual user. Your application calls Unico's APIs on behalf of the service account, so users are not directly involved. This scenario is called 'two-legged OAuth' or '2LO'. Typically, an application uses a service account when the application calls Unico's APIs to work with its own data rather than user data.

{% hint style="warning" %}
This is step zero to begin your implementation, **so do not skip this stage.**
{% endhint %}


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