# Phase 1 Impact Assessment: Authentication Flow Change

**Date**: 2025-11-20
**Architect**: Claude (Architect Agent)
**Related ADRs**: ADR-005 (updated), ADR-008 (new)
**Related Report**: /docs/reports/2025-11-20-phase-1-foundation.md

## Summary

The authentication design has been updated to require BOTH DNS TXT verification AND email verification via rel="me" discovery. This change impacts Phase 1 implementation and defines new requirements for Phase 2.

## Authentication Flow Change

### Original Design (ADR-005 v1)
- **Primary**: Email verification (user provides email)
- **Optional**: DNS TXT verification (fast-path to skip email)
- **Flow**: DNS check → if not found, request email → send code → verify code

### Updated Design (ADR-005 v2 + ADR-008)
- **Required Factor 1**: DNS TXT verification (`_gondulf.{domain}` = `verified`)
- **Required Factor 2**: Email verification via rel="me" discovery
- **Flow**: DNS check → rel="me" discovery → send code to discovered email → verify code

### Key Differences

| Aspect | Original | Updated |
|--------|----------|---------|
| DNS TXT | Optional (fast-path) | Required (first factor) |
| Email Discovery | User input | rel="me" link parsing |
| Email Verification | Optional (fallback) | Required (second factor) |
| Security Model | Single-factor | Two-factor |
| Attack Resistance | Moderate | High (requires DNS + email control) |
| Setup Complexity | Lower (email only works) | Higher (both required) |

## Phase 1 Implementation Impact

### What Phase 1 Implemented

Phase 1 successfully implemented:
- ✅ Configuration management (GONDULF_* environment variables)
- ✅ Database layer with migrations (SQLite, SQLAlchemy Core)
- ✅ In-memory code storage (TTL-based expiration)
- ✅ Email service (SMTP with STARTTLS support)
- ✅ DNS service (TXT record querying with fallback resolvers)
- ✅ Structured logging
- ✅ FastAPI application with health check endpoint
- ✅ 94.16% test coverage (96 tests passing)

### Does Phase 1 Need Changes?

**Answer: NO. Phase 1 implementation remains valid.**

#### Analysis

**Email Service** (`src/gondulf/email.py`):
- Current: Generic email sending service
- Change Impact: **None**
- Reason: Email service sends codes to any email address. Whether email is user-provided or rel="me"-discovered doesn't affect this service.
- Status: **No changes needed**

**DNS Service** (`src/gondulf/dns.py`):
- Current: TXT record verification with fallback resolvers
- Change Impact: **None**
- Reason: DNS service already implements TXT record verification as designed. Changing from "optional" to "required" is a business logic change, not a DNS service change.
- Status: **No changes needed**

**In-Memory Storage** (`src/gondulf/storage.py`):
- Current: TTL-based code storage
- Change Impact: **None**
- Reason: Storage mechanism is independent of how email is discovered or whether DNS is optional/required.
- Status: **No changes needed**

**Database Schema** (`001_initial_schema.sql`):
- Current: `domains` table with `domain`, `verification_method`, `verified_at`
- Change Impact: **Minor update needed in Phase 2**
- Reason: Schema already supports storing verification method. Will need to update from `'txt_record'` or `'email'` to `'two_factor'` when storing records.
- Status: **Schema structure OK, values will change in Phase 2**

**Configuration** (`src/gondulf/config.py`):
- Current: SMTP configuration, DNS configuration, timeouts
- Change Impact: **None immediately, optional addition in Phase 2**
- Reason: Current configuration supports both email and DNS. May want to add timeout for HTML fetching in Phase 2.
- Status: **No changes needed now**

### Phase 1 Status: APPROVED

Phase 1 implementation remains valid and does NOT require any revisions due to the authentication flow change. All Phase 1 components are foundational services that work regardless of how they're orchestrated in the authentication flow.

## Phase 2 Requirements: New Implementation Needs

Phase 2 must now implement the updated authentication flow. Here's what needs to be built:

### 1. HTML Fetching Service (NEW)

**Purpose**: Fetch user's homepage to discover rel="me" links

**Implementation**:
```python
# src/gondulf/html_fetcher.py

import requests
from typing import Optional

class HTMLFetcherService:
    """
    Fetch user's homepage over HTTPS.
    """
    def __init__(self, timeout: int = 10):
        self.timeout = timeout
        self.max_redirects = 5
        self.max_size = 5 * 1024 * 1024  # 5MB

    def fetch_site(self, domain: str) -> Optional[str]:
        """
        Fetch site HTML content.

        Args:
            domain: Domain to fetch (e.g., "example.com")

        Returns:
            HTML content as string, or None if fetch fails
        """
        url = f"https://{domain}"

        try:
            response = requests.get(
                url,
                timeout=self.timeout,
                allow_redirects=True,
                max_redirects=self.max_redirects,
                verify=True  # Enforce SSL verification
            )
            response.raise_for_status()

            # Check content size
            if len(response.content) > self.max_size:
                raise ValueError(f"Response too large: {len(response.content)} bytes")

            return response.text

        except requests.exceptions.SSLError as e:
            logger.error(f"SSL verification failed for {domain}: {e}")
            return None
        except requests.exceptions.Timeout:
            logger.error(f"Timeout fetching {domain}")
            return None
        except Exception as e:
            logger.error(f"Failed to fetch {domain}: {e}")
            return None
```

**Dependencies**:
- `requests` library (already in pyproject.toml)
- Timeout configuration (add to Config if needed)

**Tests Required**:
- Successful HTTPS fetch
- SSL verification failure
- Timeout handling
- HTTP error codes (404, 500, etc.)
- Redirect following
- Size limit enforcement

---

### 2. rel="me" Email Discovery Service (NEW)

**Purpose**: Parse HTML to discover email from rel="me" links

**Implementation**:
```python
# src/gondulf/relme.py

from bs4 import BeautifulSoup
from typing import Optional
import re

class RelMeDiscoveryService:
    """
    Discover email addresses from rel="me" links in HTML.
    """

    def discover_email(self, html_content: str) -> Optional[str]:
        """
        Parse HTML and discover email from rel="me" link.

        Args:
            html_content: HTML content as string

        Returns:
            Email address or None if not found
        """
        try:
            # Parse HTML (BeautifulSoup handles malformed HTML)
            soup = BeautifulSoup(html_content, 'html.parser')

            # Find all rel="me" links (<link> and <a> tags)
            me_links = soup.find_all('link', rel='me') + soup.find_all('a', rel='me')

            # Look for mailto: links
            for link in me_links:
                href = link.get('href', '')
                if href.startswith('mailto:'):
                    email = href.replace('mailto:', '').strip()

                    # Validate email format
                    if self._validate_email_format(email):
                        logger.info(f"Discovered email via rel='me': {email[:3]}***")
                        return email

            logger.warning("No rel='me' mailto: link found in HTML")
            return None

        except Exception as e:
            logger.error(f"Failed to parse HTML: {e}")
            return None

    def _validate_email_format(self, email: str) -> bool:
        """Validate email address format (RFC 5322 simplified)."""
        email_regex = r'^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$'

        if not re.match(email_regex, email):
            return False

        if len(email) > 254:  # RFC 5321 maximum
            return False

        if email.count('@') != 1:
            return False

        return True
```

**Dependencies**:
- `beautifulsoup4` library (add to pyproject.toml)
- `html.parser` (Python standard library)

**Tests Required**:
- Discovery from `<link rel="me">` tags
- Discovery from `<a rel="me">` tags
- Multiple rel="me" links (select first mailto)
- Malformed HTML handling
- Missing rel="me" links
- Invalid email format in link
- Edge cases (empty href, non-mailto links, etc.)

---

### 3. Domain Verification Service (UPDATED)

**Purpose**: Orchestrate two-factor verification (DNS + Email)

**Implementation**:
```python
# src/gondulf/domain_verification.py

from typing import Tuple, Optional
from .dns import DNSService
from .html_fetcher import HTMLFetcherService
from .relme import RelMeDiscoveryService
from .email import EmailService
from .storage import CodeStorage

class DomainVerificationService:
    """
    Two-factor domain verification service.

    Verifies domain ownership through:
    1. DNS TXT record verification
    2. Email verification via rel="me" discovery
    """

    def __init__(
        self,
        dns_service: DNSService,
        html_fetcher: HTMLFetcherService,
        relme_discovery: RelMeDiscoveryService,
        email_service: EmailService,
        code_storage: CodeStorage
    ):
        self.dns = dns_service
        self.html_fetcher = html_fetcher
        self.relme = relme_discovery
        self.email = email_service
        self.code_storage = code_storage

    def start_verification(self, domain: str) -> Tuple[bool, Optional[str], Optional[str]]:
        """
        Start domain verification process.

        Returns: (success, discovered_email, error_message)

        Raises HTTPException with appropriate error if verification cannot start.
        """
        # Step 1: Verify DNS TXT record
        dns_verified = self.dns.verify_txt_record(domain, "verified")
        if not dns_verified:
            error = f"DNS TXT record not found for {domain}. Please add: _gondulf.{domain} TXT verified"
            return False, None, error

        # Step 2: Fetch site and discover email
        html = self.html_fetcher.fetch_site(domain)
        if html is None:
            error = f"Could not fetch site at https://{domain}. Please ensure site is accessible via HTTPS."
            return False, None, error

        # Step 3: Discover email from rel="me"
        email = self.relme.discover_email(html)
        if email is None:
            error = 'No rel="me" mailto: link found. Please add: <link rel="me" href="mailto:you@example.com">'
            return False, None, error

        # Step 4: Generate and send verification code
        code = self._generate_code()
        self.code_storage.store(email, code, ttl=900)  # 15 minutes

        email_sent = self.email.send_verification_email(email, code)
        if not email_sent:
            error = f"Failed to send verification email to {email}. Please try again."
            return False, email, error

        # Success: code sent to discovered email
        return True, email, None

    def verify_code(self, email: str, submitted_code: str) -> Tuple[bool, str]:
        """
        Verify submitted code.

        Returns: (success, domain_or_error_message)
        """
        stored_data = self.code_storage.get(email)

        if stored_data is None:
            return False, "No verification code found. Please restart verification."

        code, domain = stored_data

        # Verify code (constant-time comparison)
        if not secrets.compare_digest(submitted_code, code):
            return False, "Invalid code. Please try again."

        # Success: mark code as used
        self.code_storage.delete(email)

        return True, domain

    def _generate_code(self) -> str:
        """Generate 6-digit verification code."""
        return ''.join(secrets.choice('0123456789') for _ in range(6))
```

**Dependencies**:
- All Phase 1 services (DNS, Email, Storage)
- New HTML fetcher service
- New rel="me" discovery service

**Tests Required**:
- Full verification flow (DNS → rel="me" → email → code)
- DNS verification failure
- Site fetch failure
- rel="me" discovery failure
- Email send failure
- Code verification success/failure
- Multiple attempts tracking
- Code expiration

---

### 4. Domain Verification UI Endpoints (NEW)

**Purpose**: HTTP endpoints for user interaction

**Implementation**:
```python
# src/gondulf/routers/verification.py

from fastapi import APIRouter, HTTPException
from pydantic import BaseModel

router = APIRouter(prefix="/verify", tags=["verification"])

class VerificationStartRequest(BaseModel):
    domain: str

class VerificationStartResponse(BaseModel):
    success: bool
    email_masked: Optional[str]  # e.g., "u***@example.com"
    error: Optional[str]

class VerificationCodeRequest(BaseModel):
    email: str
    code: str

class VerificationCodeResponse(BaseModel):
    success: bool
    domain: Optional[str]
    error: Optional[str]

@router.post("/start", response_model=VerificationStartResponse)
async def start_verification(request: VerificationStartRequest):
    """
    Start domain verification process.

    Steps:
    1. Verify DNS TXT record
    2. Discover email from rel="me"
    3. Send verification code to email
    """
    success, email, error = domain_verification_service.start_verification(request.domain)

    if not success:
        return VerificationStartResponse(success=False, email_masked=None, error=error)

    # Mask email for display: u***@example.com
    masked_email = f"{email[0]}***@{email.split('@')[1]}"

    return VerificationStartResponse(
        success=True,
        email_masked=masked_email,
        error=None
    )

@router.post("/code", response_model=VerificationCodeResponse)
async def verify_code(request: VerificationCodeRequest):
    """
    Verify submitted code.

    Returns domain if code is valid.
    """
    success, result = domain_verification_service.verify_code(request.email, request.code)

    if not success:
        return VerificationCodeResponse(success=False, domain=None, error=result)

    return VerificationCodeResponse(success=True, domain=result, error=None)
```

**Dependencies**:
- FastAPI router
- Pydantic models
- Domain verification service

**Tests Required**:
- POST /verify/start success case
- POST /verify/start with DNS failure
- POST /verify/start with rel="me" failure
- POST /verify/start with email send failure
- POST /verify/code success case
- POST /verify/code with invalid code
- POST /verify/code with expired code
- POST /verify/code with missing code

---

### 5. Authorization Endpoint Integration (UPDATED)

**Changes to Authorization Flow**:

**Before** (original design):
```
1. User enters domain (me parameter)
2. Display form: "Enter your email at {domain}"
3. User enters email manually
4. Send code, user enters code
5. Display consent screen
```

**After** (updated design):
```
1. User enters domain (me parameter)
2. Server performs two-factor verification:
   a. Verify DNS TXT record
   b. Discover email from rel="me"
   c. Send code to discovered email
3. Display code entry form (show discovered email masked)
4. User enters code
5. Display consent screen
```

**Implementation Changes**:
- Call `DomainVerificationService.start_verification()` instead of requesting email from user
- Update UI to show "Sending code to u***@example.com" instead of email input form
- Handle new error cases (DNS not found, rel="me" not found, site unreachable)

---

## Phase 2 Feature Breakdown

### New Dependencies to Add

**pyproject.toml additions**:
```toml
[project]
dependencies = [
    # ... existing dependencies
    "beautifulsoup4>=4.12.0",  # HTML parsing for rel="me" discovery
]
```

### New Source Files

1. `src/gondulf/html_fetcher.py` - HTML fetching service
2. `src/gondulf/relme.py` - rel="me" email discovery service
3. `src/gondulf/domain_verification.py` - Two-factor verification orchestration
4. `src/gondulf/routers/verification.py` - Verification endpoints (if implemented separately from authorization)

### Updated Files

1. `src/gondulf/main.py` - Register new routers, initialize new services
2. `src/gondulf/config.py` - Optional: add HTML fetch timeout config
3. Database migration (002_update_verification_method.sql) - Change domain.verification_method values

### New Test Files

1. `tests/unit/test_html_fetcher.py` - HTML fetching tests
2. `tests/unit/test_relme.py` - rel="me" discovery tests
3. `tests/unit/test_domain_verification.py` - Verification service tests
4. `tests/integration/test_verification_endpoints.py` - Verification endpoint tests

### Estimated Effort

**New Components**:
- HTML Fetcher Service: 0.5 days
- rel="me" Discovery Service: 0.5 days
- Domain Verification Service: 1 day
- Verification Endpoints: 0.5 days
- Tests (all new components): 1 day

**Total New Work**: ~3.5 days

**Authorization Endpoint** (already planned):
- Original estimate: 3-5 days
- Updated estimate: 3-5 days (same - just uses DomainVerificationService)

## Database Schema Updates

### Migration: 002_update_verification_method.sql

```sql
-- Update verification_method values from single-factor to two-factor
-- This is a data migration, not schema change

UPDATE domains
SET verification_method = 'two_factor'
WHERE verification_method IN ('txt_record', 'email');

-- No schema changes needed - 'verification_method' column already exists
```

**When to Apply**: Phase 2, before authorization endpoint implementation

## Error Message Updates

### DNS TXT Not Found

```
DNS Verification Failed

Please add this TXT record to your domain's DNS:

Type: TXT
Name: _gondulf.example.com
Value: verified

DNS changes may take up to 24 hours to propagate.

Need help? See: https://docs.gondulf.example.com/setup/dns
```

### rel="me" Not Found

```
Email Discovery Failed

Could not find a rel="me" email link on your homepage.

Please add this to your homepage (https://example.com):
<link rel="me" href="mailto:your-email@example.com">

This declares your email address for IndieAuth verification.

Learn more: https://indieweb.org/rel-me
```

### Site Unreachable

```
Site Fetch Failed

Could not fetch your site at https://example.com

Please check:
- Site is accessible via HTTPS
- SSL certificate is valid
- No firewall blocking requests

Try again once your site is accessible.
```

### Email Send Failure

```
Email Delivery Failed

Failed to send verification code to u***@example.com

Please check:
- Email address is correct in your rel="me" link
- Email server is accepting mail
- Check spam/junk folder

Try again, or contact support if the issue persists.
```

## Documentation Updates Needed

### User Documentation (Phase 2)

1. **Setup Guide**: `/docs/user/setup.md`
   - Step 1: Add DNS TXT record
   - Step 2: Add rel="me" link to homepage
   - Step 3: Test verification

2. **Troubleshooting**: `/docs/user/troubleshooting.md`
   - DNS verification failures
   - rel="me" discovery issues
   - Email delivery problems

3. **Examples**: `/docs/user/examples.md`
   - Example HTML with rel="me" link
   - Example DNS configuration (various providers)

### Developer Documentation (Phase 2)

1. **API Reference**: `/docs/api/verification.md`
   - POST /verify/start endpoint
   - POST /verify/code endpoint
   - Error codes and responses

2. **Architecture**: `/docs/architecture/domain-verification.md`
   - Two-factor verification flow diagram
   - Service interaction diagram
   - Error handling flowchart

## Security Considerations for Phase 2

### New Attack Surfaces

1. **HTML Parsing**:
   - Risk: Malicious HTML exploiting parser
   - Mitigation: BeautifulSoup handles untrusted HTML safely
   - Test: Fuzzing with malformed HTML

2. **HTTPS Fetching**:
   - Risk: SSL verification bypass
   - Mitigation: Enforce `verify=True` in requests
   - Test: Attempt to fetch site with invalid certificate (must fail)

3. **rel="me" Spoofing**:
   - Risk: Attacker adds rel="me" to compromised site
   - Mitigation: Two-factor requirement (also need DNS control)
   - Test: Verify DNS check happens BEFORE rel="me" discovery

### Security Testing Required

1. **Input Validation**:
   - Malformed domain names
   - Oversized HTML responses (>5MB)
   - Invalid email formats in rel="me" links

2. **TLS Enforcement**:
   - Verify HTTPS-only fetching
   - Verify SSL certificate validation
   - Reject sites with invalid certificates

3. **Rate Limiting** (future):
   - Prevent bulk rel="me" discovery
   - Limit verification attempts per domain

## Configuration Updates

### Optional New Config

```python
# src/gondulf/config.py

class Config:
    # ... existing config

    # HTML Fetching (optional, has sensible defaults)
    HTML_FETCH_TIMEOUT: int = 10  # seconds
    HTML_MAX_SIZE: int = 5 * 1024 * 1024  # 5MB
    HTML_MAX_REDIRECTS: int = 5
```

### Environment Variables

```bash
# .env.example additions (optional)

# HTML Fetching Configuration (optional - has defaults)
GONDULF_HTML_FETCH_TIMEOUT=10  # Timeout for fetching user's site (seconds)
GONDULF_HTML_MAX_SIZE=5242880  # Maximum HTML size (bytes, default 5MB)
GONDULF_HTML_MAX_REDIRECTS=5   # Maximum redirects to follow
```

## Testing Strategy for Phase 2

### Unit Tests

**HTML Fetcher**:
- Mock successful HTTPS response
- Mock SSL verification failure
- Mock timeout
- Mock HTTP errors (404, 500, etc.)
- Mock size limit exceeded
- Mock redirect following

**rel="me" Discovery**:
- Parse `<link rel="me" href="mailto:...">`
- Parse `<a rel="me" href="mailto:...">`
- Handle malformed HTML
- Handle missing rel="me" links
- Handle invalid email in link
- Handle multiple rel="me" links (select first)

**Domain Verification Service**:
- Full two-factor flow success
- DNS verification failure
- Site fetch failure
- rel="me" discovery failure
- Email send failure
- Code verification success/failure

### Integration Tests

**Verification Endpoints**:
- POST /verify/start with valid domain (mock services)
- POST /verify/start with DNS failure
- POST /verify/start with rel="me" failure
- POST /verify/code with valid code
- POST /verify/code with invalid code

### End-to-End Tests (Future)

- Complete verification flow with real HTML
- Authorization flow integration
- Token issuance after successful verification

## Acceptance Criteria for Phase 2

Phase 2 will be considered complete when:

1. ✅ HTML fetcher service implemented and tested
2. ✅ rel="me" discovery service implemented and tested
3. ✅ Domain verification service orchestrates two-factor verification
4. ✅ Verification endpoints return correct responses for all cases
5. ✅ Error messages are clear and actionable
6. ✅ All new tests passing (unit + integration)
7. ✅ Test coverage remains >80% overall
8. ✅ Security testing complete (HTML parsing, TLS enforcement)
9. ✅ Documentation updated (user setup guide, API reference)
10. ✅ Database migration applied successfully

## Timeline Estimate

**Phase 2 Components**:
- HTML Fetcher: 0.5 days
- rel="me" Discovery: 0.5 days
- Domain Verification Service: 1 day
- Verification Endpoints: 0.5 days
- Testing: 1 day
- Documentation: 0.5 days

**Total New Work**: ~4 days

**Authorization Endpoint** (already planned):
- Original estimate: 3-5 days
- Updated estimate: 3-5 days (uses DomainVerificationService)

**Phase 2 Total**: ~7-9 days (vs. original estimate of 3-5 days)

**Impact**: +4 days of work due to authentication flow change

## Recommendation

**Phase 1**: APPROVED as-is. No changes needed.

**Phase 2**: Proceed with implementation of:
1. HTML fetching service
2. rel="me" discovery service
3. Domain verification service (two-factor orchestration)
4. Verification endpoints
5. Updated authorization endpoint to use domain verification service

The additional work (HTML fetching + rel="me" discovery) adds ~4 days to Phase 2, bringing total Phase 2 estimate to 7-9 days instead of original 3-5 days.

## Sign-off

**Assessment Status**: Complete
**Phase 1 Impact**: None - Phase 1 approved as-is
**Phase 2 Impact**: Additional 4 days of work for new services
**Risk Level**: Low - All new work is well-scoped and testable
**Ready to Proceed**: Yes

---

**Assessment completed**: 2025-11-20
**Architect**: Claude (Architect Agent)