fix(templates): handle optional PKCE in retry links

The "Request a new code" and "Try Again" links were outputting
code_challenge=None when PKCE was not used, causing the retry
to fail with validation errors.

Now only includes PKCE parameters if code_challenge has a value.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

client_id_validation_analysis.md

@@ -0,0 +1,187 @@
+# Client ID Validation Compliance Analysis
+
+## W3C IndieAuth Specification Requirements (Section 3.2)
+
+According to the W3C IndieAuth specification, client identifiers MUST meet the following requirements:
+
+1. **Scheme**: MUST have either `https` or `http` scheme
+2. **Path**: MUST contain a path component
+3. **Path Segments**: MUST NOT contain single-dot or double-dot path segments
+4. **Query String**: MAY contain a query string component
+5. **Fragment**: MUST NOT contain a fragment component
+6. **User Info**: MUST NOT contain username or password component
+7. **Port**: MAY contain a port
+8. **Hostname**:
+   - MUST be domain names or a loopback interface
+   - MUST NOT be IPv4 or IPv6 addresses except for 127.0.0.1 or [::1]
+
+## Current Gondulf Implementation Analysis
+
+### What We Currently Validate ✅
+
+1. **Scheme Validation** (PARTIAL)
+   - ✅ We require HTTPS scheme in `normalize_client_id()`
+   - ❌ We reject HTTP completely, even for localhost (spec allows HTTP)
+   - Location: `/src/gondulf/utils/validation.py` lines 48-49
+
+2. **Query String Preservation**
+   - ✅ We preserve query strings correctly
+   - Location: `/src/gondulf/utils/validation.py` lines 58-59
+
+3. **Fragment Preservation** (BUT NOT VALIDATED)
+   - ⚠️ We preserve fragments but don't reject them
+   - Location: `/src/gondulf/utils/validation.py` lines 60-61
+
+### What We DON'T Validate ❌
+
+1. **Path Component Requirement**
+   - ❌ We don't verify that a path component exists
+   - Spec requires at least "/" as a path
+
+2. **Path Segment Validation**
+   - ❌ We don't check for single-dot (.) or double-dot (..) path segments
+   - These should be rejected per spec
+
+3. **Fragment Component**
+   - ❌ We don't reject URLs with fragments (we actually preserve them)
+   - Spec says MUST NOT contain fragment
+
+4. **User Info Component**
+   - ❌ We don't check for or reject username:password in URLs
+   - Spec says MUST NOT contain username or password
+
+5. **Hostname/IP Validation**
+   - ❌ We don't validate that hostnames are domain names
+   - ❌ We don't reject IPv4/IPv6 addresses (except 127.0.0.1 and [::1])
+   - ❌ We don't have special handling for localhost/127.0.0.1/[::1]
+
+6. **Port Support**
+   - ✅ We preserve ports correctly
+   - ⚠️ But we don't allow HTTP for localhost with ports
+
+## Reference Implementation (IndieLogin) Comparison
+
+From examining `/home/phil/Projects/indielogin.com/app/Authenticate.php`:
+
+1. Uses `\p3k\url\is_url()` for basic URL validation (line 49)
+2. Checks that client_id contains a dot OR is localhost (line 51)
+3. Validates redirect_uri domain matches client_id domain (lines 75-95)
+4. Does NOT appear to validate all spec requirements either
+
+## Non-Compliance Issues Found
+
+### Critical Issues
+
+1. **HTTP localhost support missing**
+   ```python
+   # Current code rejects all HTTP
+   if parsed.scheme != 'https':
+       raise ValueError("client_id must use https scheme")
+   ```
+   Should allow HTTP for localhost/127.0.0.1/[::1]
+
+2. **Fragment rejection missing**
+   ```python
+   # Current code preserves fragments instead of rejecting them
+   if parsed.fragment:
+       normalized += f"#{parsed.fragment}"
+   ```
+
+3. **Path component not validated**
+   - No check that path exists (at minimum "/")
+
+4. **IP address validation missing**
+   - Should reject IPs except 127.0.0.1 and [::1]
+
+### Security Implications
+
+1. **Fragment acceptance** - Could lead to confusion about actual client_id
+2. **User info not rejected** - Could expose credentials in logs
+3. **IP addresses allowed** - Could bypass domain validation
+4. **Path traversal** - Accepting ../.. could be security issue
+
+## Recommended Fixes
+
+### Priority 1: Add proper client_id validation function
+
+Create a new `validate_client_id()` function that checks ALL spec requirements:
+
+```python
+def validate_client_id(client_id: str) -> tuple[bool, str]:
+    """
+    Validate client_id per W3C IndieAuth spec Section 3.2.
+
+    Returns:
+        (is_valid, error_message)
+    """
+    try:
+        parsed = urlparse(client_id)
+
+        # 1. Check scheme
+        if parsed.scheme not in ['https', 'http']:
+            return False, "client_id must use https or http scheme"
+
+        # 2. For HTTP, only allow localhost/loopback
+        if parsed.scheme == 'http':
+            if parsed.hostname not in ['localhost', '127.0.0.1', '[::1]', '::1']:
+                return False, "HTTP scheme only allowed for localhost/127.0.0.1/[::1]"
+
+        # 3. Must have path component
+        if not parsed.path:
+            return False, "client_id must contain a path component"
+
+        # 4. Check for . or .. segments
+        path_segments = parsed.path.split('/')
+        if '.' in path_segments or '..' in path_segments:
+            return False, "client_id must not contain . or .. path segments"
+
+        # 5. Must NOT have fragment
+        if parsed.fragment:
+            return False, "client_id must not contain a fragment"
+
+        # 6. Must NOT have user info
+        if parsed.username or parsed.password:
+            return False, "client_id must not contain username or password"
+
+        # 7. Check hostname (no raw IPs except loopback)
+        if parsed.hostname:
+            # Check if it's an IP address
+            import ipaddress
+            try:
+                ip = ipaddress.ip_address(parsed.hostname)
+                # Only allow loopback IPs
+                if not ip.is_loopback:
+                    return False, f"client_id must not use IP address {parsed.hostname}"
+            except ValueError:
+                # Not an IP, that's good (it's a domain)
+                pass
+
+        return True, ""
+
+    except Exception as e:
+        return False, f"Invalid URL: {e}"
+```
+
+### Priority 2: Update normalize_client_id()
+
+Should call validate_client_id() first, then normalize.
+
+### Priority 3: Add comprehensive tests
+
+Test all validation rules with both positive and negative cases.
+
+## Conclusion
+
+**Current Status: NOT COMPLIANT** ❌
+
+Gondulf's client_id validation is currently **not compliant** with W3C IndieAuth specification Section 3.2. We have several missing validations that need to be implemented before v1.0.0 release.
+
+### Required Actions Before v1.0.0
+
+1. Implement complete `validate_client_id()` function
+2. Update `normalize_client_id()` to validate first
+3. Add support for HTTP on localhost/127.0.0.1/[::1]
+4. Add tests for all validation rules
+5. Update authorization endpoint to use new validation
+
+This is a **BLOCKING ISSUE** for v1.0.0 release as it affects spec compliance.

docs/designs/bugfix-pkce-optional-v1.0.0.md

@@ -0,0 +1,201 @@
+# Design: Make PKCE Optional in v1.0.0 (Bug Fix)
+
+Date: 2025-12-17
+Status: Ready for Implementation
+Priority: P0 (Blocking)
+
+## Problem Statement
+
+The `/authorize` endpoint currently **requires** PKCE parameters (`code_challenge` and `code_challenge_method`), which contradicts ADR-003 that explicitly states PKCE is deferred to v1.1.0.
+
+**Current behavior (lines 325-343 in authorization.py):**
+```python
+# Validate code_challenge (PKCE required)
+if not code_challenge:
+    return {"error": "invalid_request", "error_description": "code_challenge is required (PKCE)"}
+
+if code_challenge_method != "S256":
+    return {"error": "invalid_request", "error_description": "code_challenge_method must be S256"}
+```
+
+**Expected v1.0.0 behavior per ADR-003:**
+- PKCE parameters should be **optional**
+- Clients without PKCE should be able to authenticate
+- PKCE validation is deferred to v1.1.0
+
+This bug is blocking real-world IndieAuth clients that do not use PKCE.
+
+## Design Overview
+
+The fix is straightforward: remove the mandatory PKCE checks from the authorization endpoint while preserving the ability to accept and store PKCE parameters for forward compatibility.
+
+### Principle: Minimal Change
+
+This is a bug fix, not a feature. The change should be minimal and surgical:
+1. Remove the two error-returning conditionals
+2. Add validation only when PKCE parameters ARE provided
+3. Preserve all existing storage behavior
+
+## Detailed Changes
+
+### Change 1: Remove Mandatory PKCE Check
+
+**Location:** `/src/gondulf/routers/authorization.py`, lines 325-343
+
+**Current Code (to be removed):**
+```python
+# Validate code_challenge (PKCE required)
+if not code_challenge:
+    error_params = {
+        "error": "invalid_request",
+        "error_description": "code_challenge is required (PKCE)",
+        "state": state or ""
+    }
+    redirect_url = f"{redirect_uri}?{urlencode(error_params)}"
+    return RedirectResponse(url=redirect_url, status_code=302)
+
+# Validate code_challenge_method
+if code_challenge_method != "S256":
+    error_params = {
+        "error": "invalid_request",
+        "error_description": "code_challenge_method must be S256",
+        "state": state or ""
+    }
+    redirect_url = f"{redirect_uri}?{urlencode(error_params)}"
+    return RedirectResponse(url=redirect_url, status_code=302)
+```
+
+**New Code (replacement):**
+```python
+# PKCE validation (optional in v1.0.0, per ADR-003)
+# If code_challenge is provided, validate the method
+if code_challenge:
+    if code_challenge_method and code_challenge_method != "S256":
+        error_params = {
+            "error": "invalid_request",
+            "error_description": "code_challenge_method must be S256",
+            "state": state or ""
+        }
+        redirect_url = f"{redirect_uri}?{urlencode(error_params)}"
+        return RedirectResponse(url=redirect_url, status_code=302)
+    # If code_challenge provided without method, default to S256
+    if not code_challenge_method:
+        code_challenge_method = "S256"
+else:
+    # Log for future monitoring (per ADR-003 recommendation)
+    logger.info(f"Client {client_id} not using PKCE")
+```
+
+### Change 2: Handle None Values in Session Storage
+
+The `AuthSessionService.create_session()` already accepts these parameters, and the database schema likely allows NULL values. No changes needed to the service layer.
+
+**Verification:** The auth_session.py already uses these parameters directly:
+```python
+"code_challenge": code_challenge,
+"code_challenge_method": code_challenge_method,
+```
+
+If `code_challenge` is `None`, this will store NULL in the database, which is the desired behavior.
+
+### Change 3: Update Template Context (Optional Cleanup)
+
+The templates already receive `code_challenge` and `code_challenge_method` - they will now sometimes be `None` or empty. This should not cause issues as Jinja2 handles None values gracefully in form hidden fields.
+
+## Behavior Matrix
+
+| code_challenge | code_challenge_method | Result |
+|----------------|----------------------|--------|
+| None           | None                 | Proceed without PKCE |
+| None           | "S256"               | Proceed without PKCE (method ignored) |
+| "abc123..."    | None                 | Proceed with PKCE, default to S256 |
+| "abc123..."    | "S256"               | Proceed with PKCE |
+| "abc123..."    | "plain"              | ERROR: method must be S256 |
+
+## What NOT to Change
+
+1. **Token endpoint** - Already handles PKCE correctly (optional, logged but not validated per ADR-003 lines 200-203)
+2. **POST /authorize** - Already handles PKCE correctly (optional, logged but not validated per lines 856-858)
+3. **Auth session service** - Already accepts optional code_challenge parameters
+4. **Database schema** - Likely already allows NULL for these fields
+
+## Security Considerations
+
+**No security regression:**
+- ADR-003 explicitly accepted this risk for v1.0.0
+- HTTPS enforcement mitigates code interception
+- 10-minute code lifetime limits attack window
+- Single-use codes prevent replay
+
+**Forward compatibility:**
+- PKCE parameters are still stored when provided
+- v1.1.0 can enable validation without schema changes
+- Clients using PKCE today will work in v1.1.0
+
+## Testing Strategy
+
+### Unit Tests
+
+1. **Test authorization without PKCE:**
+   - Call `/authorize` without `code_challenge` - should succeed
+   - Verify session is created with NULL code_challenge
+
+2. **Test authorization with PKCE:**
+   - Call `/authorize` with valid `code_challenge` and `code_challenge_method=S256` - should succeed
+   - Verify session stores the code_challenge
+
+3. **Test PKCE with default method:**
+   - Call `/authorize` with `code_challenge` but no `code_challenge_method`
+   - Should succeed, default to S256
+
+4. **Test invalid PKCE method:**
+   - Call `/authorize` with `code_challenge` and `code_challenge_method=plain`
+   - Should return error (only S256 supported)
+
+5. **End-to-end flow without PKCE:**
+   - Complete full authorization flow without PKCE parameters
+   - Verify token can be obtained
+
+### Manual Testing
+
+1. Use a real IndieAuth client that does NOT send PKCE
+2. Verify authentication completes successfully
+
+## Acceptance Criteria
+
+1. Clients without PKCE can complete authorization flow
+2. Clients with PKCE continue to work unchanged
+3. Invalid PKCE method (not S256) is rejected
+4. PKCE parameters are stored in auth session when provided
+5. All existing tests continue to pass
+6. New tests cover optional PKCE behavior
+
+## Implementation Notes
+
+### For the Developer
+
+The fix is contained to a single location in `authorization.py`. The key insight is:
+
+1. **DELETE** the two blocks that return errors for missing PKCE
+2. **ADD** a simpler block that only validates method IF code_challenge is provided
+3. **ADD** a log statement for clients not using PKCE (monitoring per ADR-003)
+
+The rest of the codebase already handles optional PKCE correctly. This was an error in the GET /authorize validation logic only.
+
+### Estimated Effort
+
+**S (Small)** - 1-2 hours including tests
+
+### Files to Modify
+
+1. `/src/gondulf/routers/authorization.py` - Remove mandatory PKCE checks (~20 lines changed)
+
+### Files to Add
+
+1. Tests for optional PKCE behavior (or add to existing authorization tests)
+
+## References
+
+- ADR-003: `/docs/decisions/ADR-003-pkce-deferred-to-v1-1-0.md`
+- W3C IndieAuth: https://www.w3.org/TR/indieauth/ (PKCE is not mentioned, making it optional)
+- RFC 7636: https://datatracker.ietf.org/doc/html/rfc7636 (PKCE specification)

docs/reports/2025-12-17-bugfix-pkce-optional.md

@@ -0,0 +1,188 @@
+# Implementation Report: PKCE Optional Bug Fix
+
+**Date**: 2025-12-17
+**Developer**: Claude (Developer Agent)
+**Design Reference**: /home/phil/Projects/Gondulf/docs/designs/bugfix-pkce-optional-v1.0.0.md
+
+## Summary
+
+Successfully implemented the PKCE optional bug fix in the authorization endpoint. The `/authorize` endpoint was incorrectly requiring PKCE parameters (code_challenge and code_challenge_method), which contradicted ADR-003 that explicitly defers PKCE to v1.1.0. The fix makes PKCE parameters optional while maintaining validation when they are provided. All tests pass (536 passed, 5 skipped) with overall test coverage at 90.51%.
+
+## What Was Implemented
+
+### Components Modified
+
+1. **`/home/phil/Projects/Gondulf/src/gondulf/routers/authorization.py`** (lines 325-343)
+   - Replaced mandatory PKCE validation with optional validation
+   - Added default behavior for code_challenge_method (defaults to S256)
+   - Added logging for clients not using PKCE
+
+2. **`/home/phil/Projects/Gondulf/tests/integration/api/test_authorization_flow.py`**
+   - Removed test that incorrectly expected PKCE to be required (`test_missing_code_challenge_redirects_with_error`)
+   - Added comprehensive test suite for optional PKCE behavior (4 new tests)
+
+### Key Implementation Details
+
+**Authorization Endpoint Changes:**
+- Removed the error response for missing `code_challenge` parameter
+- Changed validation logic to only check `code_challenge_method` when `code_challenge` is provided
+- Added default value of "S256" for `code_challenge_method` when `code_challenge` is present but method is not specified
+- Added info-level logging when clients don't use PKCE for monitoring purposes (per ADR-003)
+
+**Test Updates:**
+- Created new test class `TestAuthorizationPKCEOptional` with 4 test scenarios
+- Tests verify all behaviors from the design's behavior matrix:
+  - Authorization without PKCE succeeds (session created with None values)
+  - Authorization with PKCE succeeds (session created with PKCE values)
+  - Authorization with code_challenge but no method defaults to S256
+  - Authorization with invalid method (not S256) is rejected
+
+## How It Was Implemented
+
+### Approach
+
+1. **Read and understood the design document** thoroughly before making any changes
+2. **Reviewed ADR-003** to understand the architectural decision behind PKCE deferral
+3. **Implemented the exact code replacement** specified in the design document
+4. **Identified and removed the incorrect test** that expected PKCE to be mandatory
+5. **Added comprehensive tests** covering all scenarios in the behavior matrix
+6. **Ran the full test suite** to verify no regressions
+
+### Implementation Order
+
+1. Modified authorization.py with the exact replacement from the design
+2. Removed the test that contradicted ADR-003
+3. Added 4 new tests for optional PKCE behavior
+4. Verified all tests pass with good coverage
+
+### Key Decisions Made
+
+All decisions were made within the bounds of the design:
+- Used exact code replacement from design document (lines 325-343)
+- Followed the behavior matrix exactly as specified
+- Applied testing standards from `/home/phil/Projects/Gondulf/docs/standards/testing.md`
+
+## Deviations from Design
+
+No deviations from design.
+
+## Issues Encountered
+
+### Challenges
+
+No significant challenges encountered. The design was clear and comprehensive, making implementation straightforward.
+
+### Unexpected Discoveries
+
+None - the implementation proceeded exactly as designed.
+
+## Test Results
+
+### Test Execution
+
+```
+============================= test session starts ==============================
+platform linux -- Python 3.11.14, pytest-9.0.1, pluggy-1.6.0
+rootdir: /home/phil/Projects/Gondulf
+configfile: pyproject.toml
+plugins: anyio-4.11.0, asyncio-1.3.0, mock-3.15.1, cov-7.0.0, Faker-38.2.0
+asyncio: mode=Mode.AUTO, debug=False
+
+================= 536 passed, 5 skipped, 39 warnings in 18.09s =================
+```
+
+### Test Coverage
+
+- **Overall Coverage**: 90.51%
+- **Coverage Tool**: pytest-cov 7.0.0
+- **Coverage Target**: 80.0% (exceeded)
+
+**Authorization Router Coverage**: 74.32%
+- The coverage drop in authorization.py is due to error handling paths that are difficult to trigger in tests (e.g., database failures, DNS failures)
+- The core PKCE logic added/modified is fully covered by the new tests
+
+### Test Scenarios
+
+#### New Tests Added (TestAuthorizationPKCEOptional)
+
+1. **`test_authorization_without_pkce_succeeds`**
+   - Verifies clients without PKCE can complete authorization
+   - Confirms session created with `code_challenge=None` and `code_challenge_method=None`
+   - Tests the primary bug fix (PKCE is optional)
+
+2. **`test_authorization_with_pkce_succeeds`**
+   - Verifies clients with PKCE continue to work unchanged
+   - Confirms session stores PKCE parameters correctly
+   - Ensures backward compatibility for PKCE-using clients
+
+3. **`test_authorization_with_pkce_defaults_to_s256`**
+   - Verifies code_challenge without method defaults to S256
+   - Confirms session stores `code_challenge_method="S256"` when not provided
+   - Tests the graceful defaulting behavior
+
+4. **`test_authorization_with_invalid_pkce_method_rejected`**
+   - Verifies invalid method (e.g., "plain") is rejected when code_challenge provided
+   - Confirms error redirect with proper OAuth error format
+   - Tests that we only support S256 method
+
+#### Modified Tests
+
+- **Removed**: `test_missing_code_challenge_redirects_with_error`
+  - This test was incorrect - it expected PKCE to be mandatory
+  - Removal aligns tests with ADR-003
+
+#### Integration Tests
+
+All existing integration tests continue to pass:
+- End-to-end authorization flows (9 tests)
+- Token exchange flows (15 tests)
+- Authorization verification flows (10 tests)
+- Response type flows (20 tests)
+
+### Test Results Analysis
+
+All tests passing: Yes (536 passed, 5 skipped)
+
+Coverage acceptable: Yes (90.51% overall, exceeds 80% requirement)
+
+Test coverage gaps: The authorization router has some uncovered error paths (DNS failures, email failures) which are difficult to trigger in integration tests without extensive mocking. These are acceptable as they are defensive error handling.
+
+Known issues: None
+
+## Technical Debt Created
+
+**Debt Item**: Authorization router error handling paths have lower coverage (74.32%)
+
+**Reason**: Many error paths involve external service failures (DNS, email) that are difficult to trigger without extensive mocking infrastructure
+
+**Suggested Resolution**:
+- Consider adding unit tests specifically for error handling paths
+- Could be addressed in v1.1.0 alongside PKCE validation implementation
+- Not blocking for this bug fix as core functionality is well-tested
+
+## Next Steps
+
+1. **Architect Review**: This implementation report is ready for review
+2. **Deployment**: Once approved, this fix can be deployed to production
+3. **Monitoring**: Monitor logs for clients not using PKCE (info-level logging added)
+4. **v1.1.0 Planning**: This fix prepares the codebase for PKCE validation in v1.1.0
+
+## Sign-off
+
+**Implementation status**: Complete
+
+**Ready for Architect review**: Yes
+
+**All acceptance criteria met**: Yes
+- Clients without PKCE can complete authorization flow ✓
+- Clients with PKCE continue to work unchanged ✓
+- Invalid PKCE method (not S256) is rejected ✓
+- PKCE parameters are stored in auth session when provided ✓
+- All existing tests continue to pass ✓
+- New tests cover optional PKCE behavior ✓
+
+**Test coverage**: 90.51% overall (exceeds 80% requirement)
+
+**Deviations from design**: None
+
+**Blockers**: None

docs/roadmap/v1.1.0.md

@@ -0,0 +1,232 @@
+# v1.1.0 Release Plan: Security & Production Hardening
+
+**Status**: Planning
+**Target Release**: Q1 2026
+**Duration**: 3-4 weeks (12-18 days)
+**Theme**: Mixed approach - 30% technical debt cleanup, 70% new features
+**Compatibility**: Backward compatible with v1.0.0, maintains single-process simplicity
+
+## Goals
+
+1. Address critical technical debt that could compound
+2. Implement security best practices (PKCE, token revocation, refresh tokens)
+3. Add production observability (Prometheus metrics)
+4. Maintain backward compatibility with v1.0.0
+5. Keep deployment simple (no Redis requirement)
+
+## Success Criteria
+
+- All technical debt items TD-001, TD-002, TD-003 resolved
+- PKCE support implemented per ADR-003
+- Token revocation and refresh functional
+- Prometheus metrics available
+- All tests passing with >90% coverage
+- Zero breaking changes for v1.0.0 clients
+- Documentation complete with migration guide
+
+## Features & Technical Debt
+
+### Phase 1: Technical Debt Cleanup (30% - 4-5 days)
+
+#### TD-001: FastAPI Lifespan Migration
+- **Effort**: <1 day
+- **Priority**: P2
+- **Type**: Technical Debt
+- **Description**: Replace deprecated `@app.on_event()` decorators with modern lifespan handlers
+- **Rationale**: Current implementation uses deprecated API that will break in future FastAPI versions
+- **Impact**: Removes deprecation warnings, future-proofs codebase
+- **Files Affected**: `src/gondulf/main.py`
+
+#### TD-002: Alembic Database Migration System
+- **Effort**: 1-2 days
+- **Priority**: P2
+- **Type**: Technical Debt
+- **Description**: Replace custom migration system with Alembic
+- **Rationale**: Current migrations are one-way only, no rollback capability
+- **Impact**: Production deployment safety, standard migration tooling
+- **Deliverables**:
+  - Alembic configuration
+  - Convert existing migrations to Alembic format
+  - Migration rollback capability
+  - Updated deployment documentation
+
+#### TD-003: Async Email Support
+- **Effort**: 1-2 days
+- **Priority**: P2
+- **Type**: Technical Debt
+- **Description**: Replace synchronous SMTP with aiosmtplib
+- **Rationale**: Current SMTP blocks request thread (1-5 sec delays during email sending)
+- **Impact**: Improved UX, non-blocking email operations
+- **Files Affected**: `src/gondulf/services/email_service.py`
+
+### Phase 2: Security Features (40% - 5-7 days)
+
+#### PKCE Support (RFC 7636)
+- **Effort**: 1-2 days
+- **Priority**: P1
+- **Type**: Feature
+- **ADR**: ADR-003 explicitly defers PKCE to v1.1.0
+- **Description**: Implement Proof Key for Code Exchange
+- **Rationale**: OAuth 2.0 security best practice, protects against authorization code interception
+- **Backward Compatible**: Yes (PKCE is optional, non-PKCE clients continue working)
+- **Implementation**:
+  - Accept `code_challenge` and `code_challenge_method` parameters in /authorize
+  - Store code challenge with authorization code
+  - Accept `code_verifier` parameter in /token endpoint
+  - Validate SHA256(code_verifier) matches stored code_challenge
+  - Update metadata endpoint to advertise PKCE support
+- **Testing**: Comprehensive tests for S256 method, optional PKCE, validation failures
+
+#### Token Revocation Endpoint (RFC 7009)
+- **Effort**: 1-2 days
+- **Priority**: P1
+- **Type**: Feature
+- **Description**: POST /token/revoke endpoint for revoking access and refresh tokens
+- **Rationale**: Security improvement - allows clients to invalidate tokens
+- **Backward Compatible**: Yes (new endpoint)
+- **Implementation**:
+  - POST /token/revoke endpoint
+  - Accept `token` and `token_type_hint` parameters
+  - Mark tokens as revoked in database
+  - Update token verification to check revocation status
+- **Testing**: Revoke access tokens, refresh tokens, invalid tokens, already-revoked tokens
+
+#### Token Refresh (RFC 6749 Section 6)
+- **Effort**: 3-5 days
+- **Priority**: P1
+- **Type**: Feature
+- **Description**: Implement refresh token grant type for long-lived sessions
+- **Rationale**: Standard OAuth 2.0 feature, enables long-lived sessions without re-authentication
+- **Backward Compatible**: Yes (optional feature, clients must opt-in)
+- **Implementation**:
+  - Generate refresh tokens alongside access tokens
+  - Store refresh tokens in database with expiration (30-90 days)
+  - Accept `grant_type=refresh_token` in /token endpoint
+  - Implement refresh token rotation (security best practice)
+  - Update metadata endpoint
+- **Testing**: Token refresh flow, rotation, expiration, revocation
+
+### Phase 3: Operational Features (30% - 3-4 days)
+
+#### Prometheus Metrics Endpoint
+- **Effort**: 1-2 days
+- **Priority**: P2
+- **Type**: Feature
+- **Description**: /metrics endpoint exposing Prometheus-compatible metrics
+- **Rationale**: Production observability, monitoring, alerting
+- **Backward Compatible**: Yes (new endpoint)
+- **Metrics**:
+  - HTTP request counters (by endpoint, method, status code)
+  - Response time histograms
+  - Active authorization sessions
+  - Token issuance/verification counters
+  - Error rates by type
+  - Database connection pool stats
+- **Implementation**: Use prometheus_client library
+- **Testing**: Metrics accuracy, format compliance
+
+#### Testing & Documentation
+- **Effort**: 2-3 days
+- **Priority**: P1
+- **Type**: Quality Assurance
+- **Deliverables**:
+  - Unit tests for all new features (>90% coverage maintained)
+  - Integration tests for PKCE, revocation, refresh flows
+  - Update API documentation
+  - Migration guide: v1.0.0 → v1.1.0
+  - Update deployment documentation
+  - Changelog for v1.1.0
+
+## Deferred to Future Releases
+
+### v1.2.0 Candidates
+
+- **Rate Limiting** - Requires Redis, breaks single-process simplicity
+  - Defer until scaling beyond single process is needed
+  - Will require Redis dependency decision
+
+- **Redis Session Storage** (TD-004) - Not critical yet
+  - Current in-memory storage works for single process
+  - Codes are short-lived (10-15 min), minimal impact from restarts
+
+- **Admin Dashboard** - Lower priority operational feature
+
+- **PostgreSQL Support** - SQLite sufficient for target scale
+
+### v2.0.0 Considerations
+
+Not committing to v2.0.0 scope yet. Will evaluate after v1.1.0 and v1.2.0 to determine if breaking changes are needed.
+
+Potential v2.0.0 candidates (breaking changes):
+- Scope-based authorization (full OAuth 2.0 authz server)
+- JWT tokens (instead of opaque tokens)
+- Required PKCE (breaking for non-PKCE clients)
+
+## Technical Debt Status
+
+After v1.1.0, remaining technical debt:
+- **TD-004: Redis for Session Storage** (deferred to when scaling needed)
+
+All other critical technical debt will be resolved.
+
+## Dependencies
+
+### External Dependencies Added
+- `aiosmtplib` - Async SMTP client
+- `alembic` - Database migration tool
+- `prometheus_client` - Metrics library
+
+### Breaking Changes
+**None** - v1.1.0 is fully backward compatible with v1.0.0
+
+## Release Checklist
+
+- [ ] Phase 1: Technical debt cleanup complete
+  - [ ] TD-001: FastAPI lifespan migration
+  - [ ] TD-002: Alembic integration
+  - [ ] TD-003: Async email support
+- [ ] Phase 2: Security features complete
+  - [ ] PKCE support implemented and tested
+  - [ ] Token revocation endpoint functional
+  - [ ] Token refresh flow working
+- [ ] Phase 3: Operational features complete
+  - [ ] Prometheus metrics endpoint
+  - [ ] Documentation updated
+  - [ ] Migration guide written
+- [ ] All tests passing (>90% coverage)
+- [ ] Security audit passed
+- [ ] Real client testing (PKCE-enabled clients)
+- [ ] Performance testing (async email, metrics overhead)
+- [ ] Docker image built and tested
+- [ ] Release notes written
+- [ ] Tag v1.1.0 and push to registry
+
+## Timeline
+
+**Week 1**: Technical debt cleanup (TD-001, TD-002, TD-003)
+**Week 2**: PKCE support + Token revocation
+**Week 3**: Token refresh implementation
+**Week 4**: Prometheus metrics + Testing + Documentation
+
+## Risk Assessment
+
+**Low Risk** - All changes are additive and backward compatible
+
+Potential risks:
+- Alembic migration conversion complexity (mitigation: thorough testing)
+- PKCE validation edge cases (mitigation: comprehensive test suite)
+- Refresh token security (mitigation: implement rotation best practices)
+
+## Version Compatibility
+
+- **v1.0.0 clients**: Fully compatible, no changes required
+- **New features**: Opt-in (PKCE, refresh tokens)
+- **Deployment**: Drop-in replacement, run migrations, no config changes required (unless using new features)
+
+## References
+
+- ADR-003: PKCE Deferred to v1.1.0
+- RFC 7636: Proof Key for Code Exchange (PKCE)
+- RFC 7009: OAuth 2.0 Token Revocation
+- RFC 6749: OAuth 2.0 Framework (Refresh Tokens)
+- Technical Debt Backlog: `/docs/roadmap/backlog.md`

pyproject.toml

@@ -1,6 +1,6 @@
 [project]
 name = "gondulf"
-version = "1.0.0"
+version = "1.0.2"
 description = "A self-hosted IndieAuth server implementation"
 readme = "README.md"
 requires-python = ">=3.10"

src/gondulf/routers/authorization.py

@@ -322,18 +322,11 @@ async def authorize_get(
         redirect_url = f"{redirect_uri}?{urlencode(error_params)}"
         return RedirectResponse(url=redirect_url, status_code=302)
 
-    # Validate code_challenge (PKCE required)
+    # PKCE validation (optional in v1.0.0, per ADR-003)
-    if not code_challenge:
+    # If code_challenge is provided, validate method is S256
-        error_params = {
+    # If not provided, proceed without PKCE
-            "error": "invalid_request",
+    if code_challenge:
-            "error_description": "code_challenge is required (PKCE)",
+        if code_challenge_method and code_challenge_method != "S256":
-            "state": state or ""
-        }
-        redirect_url = f"{redirect_uri}?{urlencode(error_params)}"
-        return RedirectResponse(url=redirect_url, status_code=302)
-
-    # Validate code_challenge_method
-    if code_challenge_method != "S256":
             error_params = {
                 "error": "invalid_request",
                 "error_description": "code_challenge_method must be S256",
@@ -341,6 +334,11 @@ async def authorize_get(
             }
             redirect_url = f"{redirect_uri}?{urlencode(error_params)}"
             return RedirectResponse(url=redirect_url, status_code=302)
+        # Default to S256 if not specified but challenge provided
+        if not code_challenge_method:
+            code_challenge_method = "S256"
+    else:
+        logger.info(f"Client {client_id} not using PKCE (optional in v1.0.0)")
 
     # Validate me parameter
     if not me:

src/gondulf/templates/verification_error.html

@@ -33,7 +33,7 @@
 {% endif %}
 
 <p>
-    <a href="/authorize?client_id={{ client_id }}&redirect_uri={{ redirect_uri }}&response_type={{ response_type }}&state={{ state }}&code_challenge={{ code_challenge }}&code_challenge_method={{ code_challenge_method }}&scope={{ scope }}&me={{ me }}">
+    <a href="/authorize?client_id={{ client_id }}&redirect_uri={{ redirect_uri }}&response_type={{ response_type }}&state={{ state }}{% if code_challenge %}&code_challenge={{ code_challenge }}&code_challenge_method={{ code_challenge_method }}{% endif %}&scope={{ scope }}&me={{ me }}">
         Try Again
     </a>
 </p>

src/gondulf/templates/verify_code.html

@@ -36,7 +36,7 @@
 
 <p class="help-text">
     Did not receive a code? Check your spam folder.
-    <a href="/authorize?client_id={{ client_id }}&redirect_uri={{ redirect_uri }}&response_type={{ response_type }}&state={{ state }}&code_challenge={{ code_challenge }}&code_challenge_method={{ code_challenge_method }}&scope={{ scope }}&me={{ me }}">
+    <a href="/authorize?client_id={{ client_id }}&redirect_uri={{ redirect_uri }}&response_type={{ response_type }}&state={{ state }}{% if code_challenge %}&code_challenge={{ code_challenge }}&code_challenge_method={{ code_challenge_method }}{% endif %}&scope={{ scope }}&me={{ me }}">
         Request a new code
     </a>
 </p>

test_client_id_spec_compliance.py

@@ -0,0 +1,93 @@
+#!/usr/bin/env python3
+"""Test script to verify client_id validation compliance with W3C IndieAuth spec Section 3.2."""
+
+import sys
+from urllib.parse import urlparse
+
+# Import the validation function
+sys.path.insert(0, '/home/phil/Projects/Gondulf/src')
+from gondulf.utils.validation import normalize_client_id
+
+
+def test_client_id(client_id: str, should_pass: bool, reason: str):
+    """Test a single client_id against the spec."""
+    try:
+        result = normalize_client_id(client_id)
+        passed = True
+        print(f"✓ Accepted: {client_id} -> {result}")
+    except ValueError as e:
+        passed = False
+        print(f"✗ Rejected: {client_id} ({str(e)})")
+
+    if passed != should_pass:
+        print(f"  ERROR: Expected {'pass' if should_pass else 'fail'}: {reason}")
+        return False
+    return True
+
+
+def main():
+    """Run comprehensive client_id validation tests."""
+    print("Testing client_id validation against W3C IndieAuth spec Section 3.2")
+    print("=" * 70)
+
+    tests = [
+        # Valid client_ids per spec
+        ("https://example.com", True, "Valid HTTPS URL with domain"),
+        ("https://example.com/", True, "Valid HTTPS URL with path /"),
+        ("https://example.com/app", True, "Valid HTTPS URL with path"),
+        ("https://example.com/app/client", True, "Valid HTTPS URL with multiple path segments"),
+        ("https://example.com?foo=bar", True, "Valid HTTPS URL with query string"),
+        ("https://example.com:8080", True, "Valid HTTPS URL with port"),
+        ("https://example.com:8080/app", True, "Valid HTTPS URL with port and path"),
+        ("http://localhost", True, "Valid HTTP localhost (loopback allowed)"),
+        ("http://localhost:3000", True, "Valid HTTP localhost with port"),
+        ("http://127.0.0.1", True, "Valid HTTP IPv4 loopback"),
+        ("http://127.0.0.1:3000", True, "Valid HTTP IPv4 loopback with port"),
+        ("http://[::1]", True, "Valid HTTP IPv6 loopback"),
+        ("http://[::1]:3000", True, "Valid HTTP IPv6 loopback with port"),
+
+        # Invalid client_ids per spec
+        ("http://example.com", False, "HTTP not allowed for non-loopback"),
+        ("https://example.com#fragment", False, "Fragment not allowed"),
+        ("https://user:pass@example.com", False, "Username/password not allowed"),
+        ("https://192.168.1.1", False, "IPv4 address not allowed (except 127.0.0.1)"),
+        ("https://[2001:db8::1]", False, "IPv6 address not allowed (except ::1)"),
+        ("https://10.0.0.1", False, "Private IPv4 not allowed"),
+        ("https://172.16.0.1", False, "Private IPv4 not allowed"),
+        ("example.com", False, "Missing scheme"),
+        ("ftp://example.com", False, "Invalid scheme (not http/https)"),
+        ("https://", False, "Missing hostname"),
+        ("https://example.com/../secret", False, "Path with .. segments not allowed"),
+        ("https://example.com/./secret", False, "Path with . segments not allowed"),
+
+        # Edge cases that spec might not explicitly cover
+        ("HTTPS://EXAMPLE.COM", True, "Uppercase scheme/host should be normalized"),
+        ("https://example.com:443", True, "Default HTTPS port should be normalized"),
+        ("http://localhost:80", True, "Default HTTP port on localhost"),
+        ("https://xn--e1afmkfd.xn--p1ai", True, "Internationalized domain names (IDN)"),
+    ]
+
+    all_passed = True
+    pass_count = 0
+    fail_count = 0
+
+    for client_id, should_pass, reason in tests:
+        if test_client_id(client_id, should_pass, reason):
+            pass_count += 1
+        else:
+            fail_count += 1
+            all_passed = False
+
+    print("\n" + "=" * 70)
+    print(f"Results: {pass_count} passed, {fail_count} failed")
+
+    if all_passed:
+        print("\n✅ All tests passed! client_id validation appears spec-compliant.")
+    else:
+        print("\n❌ Some tests failed. Review the validation logic against the spec.")
+
+    return 0 if all_passed else 1
+
+
+if __name__ == "__main__":
+    sys.exit(main())

tests/integration/api/test_authorization_flow.py

@@ -127,20 +127,6 @@ class TestAuthorizationEndpointRedirectErrors:
         assert "error=unsupported_response_type" in location
         assert "state=test123" in location
 
-    def test_missing_code_challenge_redirects_with_error(self, auth_client, valid_params, mock_happ_fetch):
-        """Test missing PKCE code_challenge redirects with error."""
-        params = valid_params.copy()
-        params["response_type"] = "code"
-        params["me"] = "https://user.example.com"
-        # Missing code_challenge
-
-        response = auth_client.get("/authorize", params=params, follow_redirects=False)
-
-        assert response.status_code == 302
-        location = response.headers["location"]
-        assert "error=invalid_request" in location
-        assert "code_challenge" in location.lower()
-
     def test_invalid_code_challenge_method_redirects_with_error(self, auth_client, valid_params, mock_happ_fetch):
         """Test invalid code_challenge_method redirects with error."""
         params = valid_params.copy()
@@ -401,6 +387,262 @@ class TestAuthorizationConsentSubmission:
             auth_app.dependency_overrides.clear()
 
 
+class TestAuthorizationPKCEOptional:
+    """Tests for optional PKCE behavior (ADR-003: PKCE deferred to v1.1.0)."""
+
+    @pytest.fixture
+    def valid_params_without_pkce(self):
+        """Valid authorization parameters WITHOUT PKCE."""
+        return {
+            "client_id": "https://app.example.com",
+            "redirect_uri": "https://app.example.com/callback",
+            "response_type": "code",
+            "state": "test123",
+            "me": "https://user.example.com",
+        }
+
+    @pytest.fixture
+    def valid_params_with_pkce(self):
+        """Valid authorization parameters WITH PKCE."""
+        return {
+            "client_id": "https://app.example.com",
+            "redirect_uri": "https://app.example.com/callback",
+            "response_type": "code",
+            "state": "test123",
+            "me": "https://user.example.com",
+            "code_challenge": "E9Melhoa2OwvFrEMTJguCHaoeK1t8URWbuGJSstw-cM",
+            "code_challenge_method": "S256",
+        }
+
+    def test_authorization_without_pkce_succeeds(self, auth_app, valid_params_without_pkce, mock_happ_fetch):
+        """Test authorization request without PKCE succeeds (PKCE is optional)."""
+        from gondulf.dependencies import (
+            get_dns_service, get_email_service, get_html_fetcher,
+            get_relme_parser, get_auth_session_service, get_database
+        )
+        from gondulf.database.connection import Database
+        from sqlalchemy import text
+        import tempfile
+
+        with tempfile.TemporaryDirectory() as tmpdir:
+            db_path = Path(tmpdir) / "test.db"
+            db = Database(f"sqlite:///{db_path}")
+            db.initialize()
+
+            now = datetime.utcnow()
+            with db.get_engine().begin() as conn:
+                conn.execute(
+                    text("""
+                        INSERT OR REPLACE INTO domains
+                        (domain, email, verification_code, verified, verified_at, last_checked, two_factor)
+                        VALUES (:domain, '', '', 1, :now, :now, 0)
+                    """),
+                    {"domain": "user.example.com", "now": now}
+                )
+
+            mock_dns = Mock()
+            mock_dns.verify_txt_record.return_value = True
+
+            mock_email = Mock()
+            mock_email.send_verification_code = Mock()
+
+            mock_html = Mock()
+            mock_html.fetch.return_value = '<html><a href="mailto:test@example.com" rel="me">Email</a></html>'
+
+            from gondulf.services.relme_parser import RelMeParser
+            mock_relme = RelMeParser()
+
+            mock_session = Mock()
+            mock_session.create_session.return_value = {
+                "session_id": "test_session_123",
+                "verification_code": "123456",
+                "expires_at": datetime.utcnow() + timedelta(minutes=10)
+            }
+
+            auth_app.dependency_overrides[get_database] = lambda: db
+            auth_app.dependency_overrides[get_dns_service] = lambda: mock_dns
+            auth_app.dependency_overrides[get_email_service] = lambda: mock_email
+            auth_app.dependency_overrides[get_html_fetcher] = lambda: mock_html
+            auth_app.dependency_overrides[get_relme_parser] = lambda: mock_relme
+            auth_app.dependency_overrides[get_auth_session_service] = lambda: mock_session
+
+            try:
+                with TestClient(auth_app) as client:
+                    response = client.get("/authorize", params=valid_params_without_pkce)
+
+                # Should succeed and show verification page
+                assert response.status_code == 200
+                assert "Verify Your Identity" in response.text
+                # Session should be created with None for code_challenge
+                mock_session.create_session.assert_called_once()
+                call_kwargs = mock_session.create_session.call_args[1]
+                assert call_kwargs["code_challenge"] is None
+                assert call_kwargs["code_challenge_method"] is None
+            finally:
+                auth_app.dependency_overrides.clear()
+
+    def test_authorization_with_pkce_succeeds(self, auth_app, valid_params_with_pkce, mock_happ_fetch):
+        """Test authorization request with PKCE succeeds."""
+        from gondulf.dependencies import (
+            get_dns_service, get_email_service, get_html_fetcher,
+            get_relme_parser, get_auth_session_service, get_database
+        )
+        from gondulf.database.connection import Database
+        from sqlalchemy import text
+        import tempfile
+
+        with tempfile.TemporaryDirectory() as tmpdir:
+            db_path = Path(tmpdir) / "test.db"
+            db = Database(f"sqlite:///{db_path}")
+            db.initialize()
+
+            now = datetime.utcnow()
+            with db.get_engine().begin() as conn:
+                conn.execute(
+                    text("""
+                        INSERT OR REPLACE INTO domains
+                        (domain, email, verification_code, verified, verified_at, last_checked, two_factor)
+                        VALUES (:domain, '', '', 1, :now, :now, 0)
+                    """),
+                    {"domain": "user.example.com", "now": now}
+                )
+
+            mock_dns = Mock()
+            mock_dns.verify_txt_record.return_value = True
+
+            mock_email = Mock()
+            mock_email.send_verification_code = Mock()
+
+            mock_html = Mock()
+            mock_html.fetch.return_value = '<html><a href="mailto:test@example.com" rel="me">Email</a></html>'
+
+            from gondulf.services.relme_parser import RelMeParser
+            mock_relme = RelMeParser()
+
+            mock_session = Mock()
+            mock_session.create_session.return_value = {
+                "session_id": "test_session_123",
+                "verification_code": "123456",
+                "expires_at": datetime.utcnow() + timedelta(minutes=10)
+            }
+
+            auth_app.dependency_overrides[get_database] = lambda: db
+            auth_app.dependency_overrides[get_dns_service] = lambda: mock_dns
+            auth_app.dependency_overrides[get_email_service] = lambda: mock_email
+            auth_app.dependency_overrides[get_html_fetcher] = lambda: mock_html
+            auth_app.dependency_overrides[get_relme_parser] = lambda: mock_relme
+            auth_app.dependency_overrides[get_auth_session_service] = lambda: mock_session
+
+            try:
+                with TestClient(auth_app) as client:
+                    response = client.get("/authorize", params=valid_params_with_pkce)
+
+                # Should succeed and show verification page
+                assert response.status_code == 200
+                assert "Verify Your Identity" in response.text
+                # Session should be created with PKCE parameters
+                mock_session.create_session.assert_called_once()
+                call_kwargs = mock_session.create_session.call_args[1]
+                assert call_kwargs["code_challenge"] == "E9Melhoa2OwvFrEMTJguCHaoeK1t8URWbuGJSstw-cM"
+                assert call_kwargs["code_challenge_method"] == "S256"
+            finally:
+                auth_app.dependency_overrides.clear()
+
+    def test_authorization_with_pkce_defaults_to_s256(self, auth_app, mock_happ_fetch):
+        """Test authorization with code_challenge but no method defaults to S256."""
+        from gondulf.dependencies import (
+            get_dns_service, get_email_service, get_html_fetcher,
+            get_relme_parser, get_auth_session_service, get_database
+        )
+        from gondulf.database.connection import Database
+        from sqlalchemy import text
+        import tempfile
+
+        params = {
+            "client_id": "https://app.example.com",
+            "redirect_uri": "https://app.example.com/callback",
+            "response_type": "code",
+            "state": "test123",
+            "me": "https://user.example.com",
+            "code_challenge": "E9Melhoa2OwvFrEMTJguCHaoeK1t8URWbuGJSstw-cM",
+            # No code_challenge_method - should default to S256
+        }
+
+        with tempfile.TemporaryDirectory() as tmpdir:
+            db_path = Path(tmpdir) / "test.db"
+            db = Database(f"sqlite:///{db_path}")
+            db.initialize()
+
+            now = datetime.utcnow()
+            with db.get_engine().begin() as conn:
+                conn.execute(
+                    text("""
+                        INSERT OR REPLACE INTO domains
+                        (domain, email, verification_code, verified, verified_at, last_checked, two_factor)
+                        VALUES (:domain, '', '', 1, :now, :now, 0)
+                    """),
+                    {"domain": "user.example.com", "now": now}
+                )
+
+            mock_dns = Mock()
+            mock_dns.verify_txt_record.return_value = True
+
+            mock_email = Mock()
+            mock_email.send_verification_code = Mock()
+
+            mock_html = Mock()
+            mock_html.fetch.return_value = '<html><a href="mailto:test@example.com" rel="me">Email</a></html>'
+
+            from gondulf.services.relme_parser import RelMeParser
+            mock_relme = RelMeParser()
+
+            mock_session = Mock()
+            mock_session.create_session.return_value = {
+                "session_id": "test_session_123",
+                "verification_code": "123456",
+                "expires_at": datetime.utcnow() + timedelta(minutes=10)
+            }
+
+            auth_app.dependency_overrides[get_database] = lambda: db
+            auth_app.dependency_overrides[get_dns_service] = lambda: mock_dns
+            auth_app.dependency_overrides[get_email_service] = lambda: mock_email
+            auth_app.dependency_overrides[get_html_fetcher] = lambda: mock_html
+            auth_app.dependency_overrides[get_relme_parser] = lambda: mock_relme
+            auth_app.dependency_overrides[get_auth_session_service] = lambda: mock_session
+
+            try:
+                with TestClient(auth_app) as client:
+                    response = client.get("/authorize", params=params)
+
+                # Should succeed and default to S256
+                assert response.status_code == 200
+                mock_session.create_session.assert_called_once()
+                call_kwargs = mock_session.create_session.call_args[1]
+                assert call_kwargs["code_challenge_method"] == "S256"
+            finally:
+                auth_app.dependency_overrides.clear()
+
+    def test_authorization_with_invalid_pkce_method_rejected(self, auth_client, mock_happ_fetch):
+        """Test authorization with code_challenge and invalid method is rejected."""
+        params = {
+            "client_id": "https://app.example.com",
+            "redirect_uri": "https://app.example.com/callback",
+            "response_type": "code",
+            "state": "test123",
+            "me": "https://user.example.com",
+            "code_challenge": "E9Melhoa2OwvFrEMTJguCHaoeK1t8URWbuGJSstw-cM",
+            "code_challenge_method": "plain",  # Invalid - only S256 supported
+        }
+
+        response = auth_client.get("/authorize", params=params, follow_redirects=False)
+
+        # Should redirect with error
+        assert response.status_code == 302
+        location = response.headers["location"]
+        assert "error=invalid_request" in location
+        assert "S256" in location
+
+
 class TestAuthorizationSecurityHeaders:
     """Tests for security headers on authorization endpoints."""
 

uv.lock

@@ -431,7 +431,7 @@ wheels = [
 
 [[package]]
 name = "gondulf"
-version = "1.0.0rc1"
+version = "1.0.1"
 source = { editable = "." }
 dependencies = [
     { name = "aiosmtplib" },