> For the complete documentation index, see [llms.txt](https://docs.developer.singpass.gov.sg/docs/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.developer.singpass.gov.sg/docs/technical-specifications/singpass-authentication-api.md).

# (Legacy) Pre-FAPI 2.0 API Specifications

{% hint style="danger" %}
All Login and Myinfo apps must follow Singpass' [FAPI 2.0-compliant authentication API](/docs/technical-specifications/integration-guide.md) by 31 Dec 2026.

The specifications on this page apply to you only if you are maintaining an existing Login / Myinfo (v5) integration. We encourage you to [migrate](/docs/technical-specifications/migration-guides/login-myinfo-v5-apps.md) early to avoid service disruptions.
{% endhint %}

The purpose of this guide is to describe the necessary APIs that Relying Parties (RPs) must invoke to facilitate an Open ID Connect (OIDC) authentication for a Singpass user via the Redirect Authentication Flow.

RPs are to implement the following steps:

**Frontend:**

* Step 1a: Redirect to [Authorization endpoint](https://github.com/SingpassPX/dev-docs/blob/main/technical-specifications/singpass-authentication-api/1.-authorization-endpoint).

**Backend:**

* Step 4: Exchange auth code with ID token (involves client authentication) using [Token endpoint](https://github.com/SingpassPX/dev-docs/blob/main/technical-specifications/singpass-authentication-api/2.-token-endpoint).


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