Home Realm Discovery (HRD)

Home Realm Discovery enables automatic routing of users to their organization’s identity provider based on their email domain.

Overview

When a user enters their email address, HRD checks if the email domain is associated with a configured upstream identity provider. If a match is found, the user is redirected to their organization’s SSO provider instead of seeing the password login form.

sequenceDiagram
    participant User
    participant Client
    participant AuthOS
    participant IdP

    User->>Client: Enter email
    Client->>AuthOS: POST /api/auth/lookup-email
    AuthOS-->>Client: {redirect_to: "github", org: "acme"}
    Client->>AuthOS: GET /auth/github?org=acme&service=app
    AuthOS-->>IdP: Redirect to IdP
    IdP-->>AuthOS: OAuth callback
    AuthOS-->>Client: Tokens

Endpoints

POST /api/auth/lookup-email

Look up email domain to determine authentication method.

Synopsis

Property	Value
Authentication	Public
Rate Limit	10 requests/minute per IP
Idempotent	Yes

Request Body

Field	Type	Required	Description
`email`	`string`	Yes	User’s email address
`org_slug`	`string`	Yes	Organization slug
`service_slug`	`string`	Yes	Service slug

Example Request

curl -X POST https://sso.example.com/api/auth/lookup-email \
  -H "Content-Type: application/json" \
  -d '{
    "email": "user@acme.com",
    "org_slug": "acme-corp",
    "service_slug": "main-app"
  }'

Response - SSO Redirect Required (200 OK)

{
  "method": "redirect",
  "provider": "github",
  "redirect_url": "/auth/github?org=acme-corp&service=main-app"
}

Response - Password Login (200 OK)

{
  "method": "password"
}

Response Fields

Field	Type	Description
`method`	`string`	`"redirect"` or `"password"`
`provider`	`string`	OAuth provider name (when method is redirect)
`redirect_url`	`string`	URL to redirect user to (when method is redirect)

Errors

Status	Code	Condition
`400`	`BAD_REQUEST`	Invalid email format
`404`	`NOT_FOUND`	Organization or service not found

Configuring HRD

Step 1: Verify Domain Ownership

Before enabling HRD for a domain, you must verify ownership:

curl -X POST https://sso.example.com/api/organizations/acme-corp/domains \
  -H "Authorization: Bearer {jwt}" \
  -H "Content-Type: application/json" \
  -d '{
    "domain": "acme.com"
  }'

Response:

{
  "domain": "acme.com",
  "verification_token": "authos-verify=abc123def456",
  "verified": false
}

Add the verification token as a TXT record:

_authos-verify.acme.com TXT "authos-verify=abc123def456"

Step 2: Verify the Domain

curl -X POST https://sso.example.com/api/organizations/acme-corp/domains/acme.com/verify \
  -H "Authorization: Bearer {jwt}"

Step 3: Configure Upstream Provider

curl -X POST https://sso.example.com/api/organizations/acme-corp/upstream-providers \
  -H "Authorization: Bearer {jwt}" \
  -H "Content-Type: application/json" \
  -d '{
    "provider": "saml",
    "name": "Okta SSO",
    "domains": ["acme.com"],
    "config": {
      "idp_metadata_url": "https://acme.okta.com/app/.../sso/saml/metadata",
      "sp_entity_id": "https://sso.example.com/saml/acme-corp"
    }
  }'

Supported Providers

Provider	Type	Configuration
GitHub	OAuth 2.0	Client ID, Client Secret
Google	OAuth 2.0	Client ID, Client Secret
Microsoft	OAuth 2.0	Client ID, Client Secret, Tenant ID
SAML	SAML 2.0	IDP Metadata URL or manual config

SSO Enforcement

When HRD is configured for a domain, you can optionally enforce SSO:

curl -X PATCH https://sso.example.com/api/organizations/acme-corp/upstream-providers/{id} \
  -H "Authorization: Bearer {jwt}" \
  -H "Content-Type: application/json" \
  -d '{
    "enforce_sso": true
  }'

With enforcement enabled:

Users with matching email domains must authenticate via SSO
Password login is disabled for these users
Password reset is disabled for these users

Client Integration

React Example

import { useState } from 'react';

function LoginForm() {
  const [email, setEmail] = useState('');
  const [showPassword, setShowPassword] = useState(false);

  async function handleEmailSubmit(e) {
    e.preventDefault();
    
    const response = await fetch('/api/auth/lookup-email', {
      method: 'POST',
      headers: { 'Content-Type': 'application/json' },
      body: JSON.stringify({
        email,
        org_slug: 'acme-corp',
        service_slug: 'main-app'
      })
    });
    
    const result = await response.json();
    
    if (result.method === 'redirect') {
      // Redirect to SSO provider
      window.location.href = result.redirect_url;
    } else {
      // Show password field
      setShowPassword(true);
    }
  }

  return (
    <form onSubmit={handleEmailSubmit}>
      <input
        type="email"
        value={email}
        onChange={(e) => setEmail(e.target.value)}
        placeholder="Enter your email"
      />
      {showPassword && (
        <input type="password" placeholder="Password" />
      )}
      <button type="submit">
        {showPassword ? 'Sign In' : 'Continue'}
      </button>
    </form>
  );
}

Security Considerations

Domain Verification Required - HRD only routes verified domains
No Email Enumeration - Always returns a response regardless of user existence
Rate Limited - Prevents domain probing attacks
HTTPS Required - All HRD endpoints require HTTPS