Login.gov Authentication API

SAML SSO request endpoint.

Documentation GitHub OpenAPI

Business capability

Citizen Identity & Authentication BC-3220.20

Operations 1

GET /api/saml/auth2026 Initiate SAML SSO (HTTP-Redirect) #

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OpenAPI Specification

openapi: 3.2.0
info:
  title: Login.gov SAML 2.0 Authentication API
  version: 2026-01
  description: 'Login.gov also supports SAML 2.0 for relying parties that prefer enterprise federation

    semantics over OIDC.'
  contact:
    name: Login.gov Partner Support
    url: https://developers.login.gov
    email: partners@login.gov
  license:
    name: Public Domain (U.S. Government Work)
    url: https://www.usa.gov/government-works
servers:
- url: https://idp.int.identitysandbox.gov
  description: Sandbox (integration) environment
- url: https://secure.login.gov
  description: Production environment
tags:
- name: Authentication
  description: SAML SSO request endpoint.
paths:
  /api/saml/auth2026:
    get:
      tags:
      - Authentication
      summary: Initiate SAML SSO (HTTP-Redirect)
      operationId: samlSso
      description: 'Accepts a Base64-encoded, DEFLATE-compressed `SAMLRequest` via HTTP-Redirect.

        The user authenticates with Login.gov and the IdP responds with a signed SAML

        assertion POSTed to the SP''s Assertion Consumer Service URL.'
      parameters:
      - name: SAMLRequest
        in: query
        required: true
        description: Base64-encoded DEFLATE-compressed AuthnRequest.
        schema:
          type: string
      - name: RelayState
        in: query
        required: false
        description: Opaque value echoed back in the SAML response.
        schema:
          type: string
      - name: SigAlg
        in: query
        required: false
        description: Signature algorithm URI when the request is signed.
        schema:
          type: string
      - name: Signature
        in: query
        required: false
        description: Base64-encoded signature over the request.
        schema:
          type: string
      responses:
        '200':
          description: Login.gov sign-in UI is rendered to the end user.
        '302':
          description: Redirect to authentication challenge or to SP ACS with the signed SAML response.

Login.gov Authentication API

Operations 1

Documentation

Specifications

Schemas & Data

Other Resources