Login Gov

login-gov

Federal identity provider integration using login.gov. Covers OIDC (preferred) and SAML, private_key_jwt authentication, assurance level selection, and the full token exchange flow.

When to use

• Integrating a web or mobile app with login.gov for federal SSO
• Choosing between auth-only, identity-verified, and PIV/CAC assurance levels
• Implementing OIDC authorization code + private_key_jwt flow
• Setting up sandbox vs production environments
• Requesting user attributes (email, phone, SSN, x509/PIV)
• Debugging invalid_client, invalid_request, or token validation errors

Do NOT use for:

• Non-federal identity providers (Okta, Auth0, Cognito — use their own SDKs)
• SAML SP setup (login.gov supports SAML but OIDC is preferred; ask user to confirm)
• Private-sector applications (login.gov is US federal agencies only)

Endpoints

Key endpoints from discovery:

• Authorization: https://idp.int.identitysandbox.gov/openid_connect/authorize
• Token: https://idp.int.identitysandbox.gov/api/openid_connect/token
• UserInfo: https://idp.int.identitysandbox.gov/api/openid_connect/userinfo
• JWKS: https://idp.int.identitysandbox.gov/api/openid_connect/certs

Authentication methods

Web apps — private_key_jwt (required)

Generate a 2048-bit RSA key pair. Register the public certificate in the Partner Portal. Sign client assertions with the private key using RS256.

# Generate key pair
openssl genrsa -out private.pem 2048
openssl req -new -x509 -key private.pem -out public.crt -days 365 \
  -subj "/C=US/ST=DC/L=Washington/O=Agency/CN=myapp.agency.gov"

# View public key for Partner Portal upload
cat public.crt

Native mobile apps — PKCE (RFC 7636)

Generate a code_verifier (43–128 URL-safe random chars), hash it:

code_challenge = BASE64URL(SHA256(code_verifier))

Pass code_challenge and code_challenge_method=S256 in the authorization request.

Explicitly NOT supported

• client_secret / client_secret_post / client_secret_basic
• Implicit flow (response_type=token)

ACR values — choose the right level

AAL (Authentication Assurance Level) modifiers — combine with ACR:

Pass multiple ACR values space-separated in the acr_values parameter.

Step 1 — Authorization request

GET https://idp.int.identitysandbox.gov/openid_connect/authorize
  ?acr_values=urn:acr.login.gov:auth-only
  &client_id=YOUR_CLIENT_ID
  &nonce=RANDOM_22_CHAR_MIN
  &prompt=select_account
  &redirect_uri=https://yourapp.agency.gov/auth/callback
  &response_type=code
  &scope=openid+email+profile
  &state=RANDOM_22_CHAR_MIN

Rules:

• state and nonce must be ≥ 22 characters — login.gov will reject shorter values
• prompt=select_account is required (no other values supported)
• redirect_uri must exactly match a registered URI in the Partner Portal
• Store state in session; store nonce for id_token validation

Step 2 — Handle the callback

GET https://yourapp.agency.gov/auth/callback
  ?code=AUTH_CODE
  &state=STATE_FROM_STEP1

Verify state matches the value you stored. Then exchange the code for tokens.

Step 3 — Token exchange

POST https://idp.int.identitysandbox.gov/api/openid_connect/token
Content-Type: application/x-www-form-urlencoded

client_assertion=SIGNED_JWT
&client_assertion_type=urn:ietf:params:oauth:client-assertion-type:jwt-bearer
&code=AUTH_CODE_FROM_CALLBACK
&grant_type=authorization_code

Build the client_assertion JWT

import jwt, time, uuid
from cryptography.hazmat.primitives.serialization import load_pem_private_key

private_key = load_pem_private_key(open("private.pem", "rb").read(), password=None)

claims = {
    "iss": CLIENT_ID,          # your client_id
    "sub": CLIENT_ID,          # also client_id
    "aud": "https://idp.int.identitysandbox.gov/api/openid_connect/token",
    "jti": str(uuid.uuid4()),  # unique per request
    "exp": int(time.time()) + 300,  # 5 minutes max
}

assertion = jwt.encode(claims, private_key, algorithm="RS256")

Token response

{
  "access_token": "TOKEN",
  "token_type": "Bearer",
  "expires_in": 900,
  "id_token": "SIGNED_JWT"
}

Validate the id_token

1. Fetch login.gov's public keys from the JWKS endpoint
2. Verify signature using RS256 with the matching key (kid header)
3. Verify iss = login.gov IdP URL
4. Verify aud = your client_id
5. Verify nonce = the nonce you sent in Step 1
6. Verify exp is in the future

Step 4 — Fetch user attributes

GET https://idp.int.identitysandbox.gov/api/openid_connect/userinfo
Authorization: Bearer ACCESS_TOKEN

Response attributes depend on scopes requested:

Note: social_security_number and identity attributes require urn:acr.login.gov:verified or higher. Login.gov will reject the request if the ACR level doesn't support the requested scope.

Sandbox setup

1. Register at https://dashboard.int.identitysandbox.gov
2. Create an app — get a client_id
3. Upload your public.crt
4. Set redirect_uri values (can be http://localhost for dev)
5. Test users: create accounts at https://idp.int.identitysandbox.gov
6. For IAL2 testing: the sandbox has a bypass — enter any SSN/address and it will pass

Production deployment checklist

• Inter-Agency Agreement (IAA) signed with GSA
• Production app registered in https://dashboard.login.gov
• Production key pair generated (separate from sandbox)
• Redirect URIs use HTTPS with valid TLS
• state and nonce are cryptographically random, stored server-side
• id_token signature validation implemented
• sub (UUID) used as the stable user identifier — not email (email can change)
• Logout: redirect to https://secure.login.gov/openid_connect/logout?client_id=...&post_logout_redirect_uri=...&state=...

Common errors

Example prompts

• "How do I integrate our agency web app with login.gov for federal SSO?"
• "Generate the private_key_jwt client assertion JWT for the token exchange."
• "What ACR value do I use if I need identity verification but not facial recognition?"
• "My token request returns invalid_client. What could cause that?"
• "How do I request the user's SSN and address attributes after they authenticate?"
• "Walk me through setting up the login.gov sandbox — discovery URL, test users, IAL2 bypass."
• "What's the production deployment checklist before we go live with login.gov?"

Related skills

• arcgis-enterprise-k8s — if fronting ArcGIS with federal identity via login.gov
• ubuntu24-stig — OS hardening for the server running the integration