# (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](/docs/technical-specifications/singpass-authentication-api/1.-authorization-endpoint.md).

**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).


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://docs.developer.singpass.gov.sg/docs/technical-specifications/singpass-authentication-api.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.