fix: Use authorization endpoint for IndieAuth code verification (v0.9.4)

IndieAuth authentication-only flows should redeem the code at the
authorization endpoint, not the token endpoint. The token endpoint
is only for authorization flows that need access tokens.

- Remove grant_type parameter (only needed for token flows)
- Change endpoint from /token to /authorize
- Update debug logging to reflect code verification flow

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

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

CHANGELOG.md

@@ -7,6 +7,28 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+## [0.9.4] - 2025-11-22
+
+### Fixed
+- **IndieAuth authentication endpoint correction**: Changed code redemption from token endpoint to authorization endpoint
+  - Per IndieAuth spec: authentication-only flows use `/authorize`, not `/token`
+  - StarPunk only needs identity verification, not access tokens
+  - Removed unnecessary `grant_type` parameter (only needed for token endpoint)
+  - Updated debug logging to reflect "code verification" terminology
+  - Fixes authentication with IndieLogin.com and spec-compliant providers
+
+### Changed
+- Code redemption now POSTs to `/authorize` endpoint instead of `/token`
+- Log messages updated from "token exchange" to "code verification"
+
+## [0.9.3] - 2025-11-22
+
+### Fixed
+- **IndieAuth token exchange missing grant_type**: Added required `grant_type=authorization_code` parameter to token exchange request
+  - OAuth 2.0 spec requires this parameter for authorization code flow
+  - Some IndieAuth providers reject token exchange without this parameter
+  - Fixes authentication failures with spec-compliant IndieAuth providers
+
 ## [0.9.2] - 2025-11-22
 
 ### Fixed

docs/decisions/ADR-022-indieauth-authentication-endpoint-correction.md

@@ -0,0 +1,188 @@
+# ADR-022: IndieAuth Authentication Endpoint Correction
+
+## Status
+Accepted
+
+## Context
+
+StarPunk is encountering authentication failures with certain IndieAuth providers (specifically gondulf.thesatelliteoflove.com). After investigation, we discovered that StarPunk is incorrectly using the **token endpoint** for authentication-only flows, when it should be using the **authorization endpoint**.
+
+### The Problem
+
+When attempting to authenticate with gondulf.thesatelliteoflove.com, the provider returns:
+```json
+{
+  "error": "invalid_grant",
+  "error_description": "Authorization code must be redeemed at the authorization endpoint"
+}
+```
+
+StarPunk is currently sending authentication code redemption requests to `/token` when it should be sending them to the authorization endpoint for authentication-only flows.
+
+### IndieAuth Specification Analysis
+
+According to the W3C IndieAuth specification (https://www.w3.org/TR/indieauth/):
+
+1. **Authentication-only flows** (Section 5.4):
+   - Used when the client only needs to verify user identity
+   - Code redemption happens at the **authorization endpoint**
+   - No `grant_type` parameter is used
+   - Response contains only `{"me": "user-url"}`
+
+2. **Authorization flows** (Section 6.3):
+   - Used when the client needs an access token for API access
+   - Code redemption happens at the **token endpoint**
+   - Requires `grant_type=authorization_code` parameter
+   - Response contains access token and user identity
+
+### Current StarPunk Implementation
+
+StarPunk's current code in `/home/phil/Projects/starpunk/starpunk/auth.py` (lines 410-419):
+
+```python
+token_exchange_data = {
+    "grant_type": "authorization_code",  # WRONG for authentication-only
+    "code": code,
+    "client_id": current_app.config["SITE_URL"],
+    "redirect_uri": f"{current_app.config['SITE_URL']}auth/callback",
+    "code_verifier": code_verifier,  # PKCE verification
+}
+
+token_url = f"{current_app.config['INDIELOGIN_URL']}/token"  # WRONG endpoint
+```
+
+This implementation has two errors:
+1. Uses `/token` endpoint instead of authorization endpoint
+2. Includes `grant_type` parameter which should not be present for authentication-only flows
+
+## Decision
+
+StarPunk must correct its IndieAuth authentication implementation to comply with the specification:
+
+1. **Use the authorization endpoint** for code redemption in authentication-only flows
+2. **Remove the `grant_type` parameter** from authentication requests
+3. **Keep PKCE parameters** (`code_verifier`) as they are still required
+
+## Rationale
+
+### Why This Matters
+
+1. **Standards Compliance**: The IndieAuth specification clearly distinguishes between authentication and authorization flows
+2. **Provider Compatibility**: Some providers (like gondulf) strictly enforce the specification
+3. **Correct Semantics**: StarPunk only needs to verify admin identity, not obtain an access token
+
+### Authentication vs Authorization
+
+StarPunk's admin login is an **authentication-only** use case:
+- We only need to verify the admin's identity (`me` URL)
+- We don't need an access token to access external resources
+- We create our own session after successful authentication
+
+This is fundamentally different from Micropub client authorization where:
+- External clients need access tokens
+- Tokens are used to authorize API access
+- The token endpoint is the correct choice
+
+## Implementation
+
+### Required Changes
+
+In `/home/phil/Projects/starpunk/starpunk/auth.py`, the `handle_callback` function must be updated:
+
+```python
+def handle_callback(code: str, state: str, iss: Optional[str] = None) -> Optional[str]:
+    # ... existing state verification code ...
+
+    # Prepare authentication request (NOT token exchange)
+    auth_data = {
+        # NO grant_type parameter for authentication-only flows
+        "code": code,
+        "client_id": current_app.config["SITE_URL"],
+        "redirect_uri": f"{current_app.config['SITE_URL']}auth/callback",
+        "code_verifier": code_verifier,  # PKCE verification still required
+    }
+
+    # Use authorization endpoint (NOT token endpoint)
+    # The same endpoint used for the initial authorization request
+    auth_url = f"{current_app.config['INDIELOGIN_URL']}/auth"  # or /authorize
+
+    # Exchange code for identity (authentication-only)
+    response = httpx.post(
+        auth_url,
+        data=auth_data,
+        timeout=10.0,
+    )
+
+    # Response will be: {"me": "https://user.example.com"}
+    # NOT an access token response
+```
+
+### Endpoint Discovery Consideration
+
+IndieAuth providers may use different paths for their authorization endpoint:
+- IndieLogin.com uses `/auth`
+- Some providers use `/authorize`
+- The gondulf provider appears to use its root domain as the authorization endpoint
+
+The correct approach is to:
+1. Discover the authorization endpoint from the provider's metadata
+2. Use the same endpoint for both authorization initiation and code redemption
+3. Store the discovered endpoint during the initial authorization request
+
+## Consequences
+
+### Positive
+- **Specification Compliance**: Correctly implements IndieAuth authentication flow
+- **Provider Compatibility**: Works with strict IndieAuth implementations
+- **Semantic Correctness**: Uses the right flow for the use case
+
+### Negative
+- **Breaking Change**: May affect compatibility with providers that accept both endpoints
+- **Testing Required**: Need to verify with multiple IndieAuth providers
+
+### Migration Impact
+- Existing sessions remain valid (no database changes)
+- Only affects new login attempts
+- Should be transparent to users
+
+## Testing Strategy
+
+Test with multiple IndieAuth providers:
+1. **IndieLogin.com** - Current provider (should continue working)
+2. **gondulf.thesatelliteoflove.com** - Strict implementation
+3. **tokens.indieauth.com** - Token-only endpoint (should fail for auth)
+4. **Self-hosted implementations** - Various compliance levels
+
+## Alternatives Considered
+
+### Alternative 1: Support Both Endpoints
+Attempt token endpoint first, fall back to authorization endpoint on failure.
+- **Pros**: Maximum compatibility
+- **Cons**: Not specification-compliant, adds complexity
+- **Verdict**: Rejected - violates standards
+
+### Alternative 2: Make Endpoint Configurable
+Allow admin to configure which endpoint to use.
+- **Pros**: Flexible for different providers
+- **Cons**: Confusing for users, not needed if we follow spec
+- **Verdict**: Rejected - specification is clear
+
+### Alternative 3: Always Use Token Endpoint
+Continue current implementation, document incompatibility.
+- **Pros**: No code changes needed
+- **Cons**: Violates specification, limits provider choice
+- **Verdict**: Rejected - incorrect implementation
+
+## References
+
+- [IndieAuth Specification Section 5.4](https://www.w3.org/TR/indieauth/#authentication-response): Authorization Code Verification for authentication flows
+- [IndieAuth Specification Section 6.3](https://www.w3.org/TR/indieauth/#token-response): Token Endpoint for authorization flows
+- [IndieAuth Authentication vs Authorization](https://indieweb.org/IndieAuth#Authentication_vs_Authorization): Community documentation
+- [ADR-021: IndieAuth Provider Strategy](/home/phil/Projects/starpunk/docs/decisions/ADR-021-indieauth-provider-strategy.md): Related architectural decision
+
+---
+
+**Document Version**: 1.0
+**Created**: 2025-11-22
+**Author**: StarPunk Architecture Team
+**Status**: Accepted

docs/decisions/ADR-022-indieauth-token-exchange-compliance.md

@@ -0,0 +1,84 @@
+# ADR-022: IndieAuth Token Exchange Compliance
+
+## Status
+Accepted
+
+## Context
+StarPunk's IndieAuth implementation is failing to authenticate with certain providers (specifically gondulf.thesatelliteoflove.com) during the token exchange phase. The provider is rejecting our token exchange requests with a "missing grant_type" error.
+
+Our current implementation sends:
+- `code`
+- `client_id`
+- `redirect_uri`
+- `code_verifier` (for PKCE)
+
+But does NOT include `grant_type=authorization_code`.
+
+## Decision
+StarPunk MUST include `grant_type=authorization_code` in all token exchange requests to be compliant with both OAuth 2.0 RFC 6749 and IndieAuth specifications.
+
+## Rationale
+
+### OAuth 2.0 RFC 6749 Compliance
+RFC 6749 Section 4.1.3 explicitly states that `grant_type` is a REQUIRED parameter with the value MUST be set to "authorization_code" for the authorization code grant flow.
+
+### IndieAuth Specification
+While the IndieAuth specification (W3C TR) doesn't use explicit RFC 2119 language (MUST/REQUIRED) for the grant_type parameter, it:
+1. Lists `grant_type=authorization_code` as part of the token request parameters in Section 6.3.1
+2. Shows it in all examples (Example 12)
+3. States that IndieAuth "builds upon the OAuth 2.0 [RFC6749] Framework"
+
+Since IndieAuth builds on OAuth 2.0, and OAuth 2.0 requires this parameter, IndieAuth implementations should include it.
+
+### Provider Compliance
+The provider (gondulf.thesatelliteoflove.com) is **correctly following the specifications** by requiring the `grant_type` parameter.
+
+## Consequences
+
+### Positive
+- Full compliance with OAuth 2.0 RFC 6749
+- Compatibility with all spec-compliant IndieAuth providers
+- Clear, standard-compliant token exchange requests
+
+### Negative
+- Requires immediate code change to add the missing parameter
+- May reveal other non-compliant providers that don't check for this parameter
+
+## Implementation Requirements
+
+The token exchange request MUST include these parameters:
+```
+grant_type=authorization_code  # REQUIRED by OAuth 2.0
+code={authorization_code}      # REQUIRED
+client_id={client_url}         # REQUIRED
+redirect_uri={redirect_url}    # REQUIRED if used in initial request
+me={user_profile_url}          # REQUIRED by IndieAuth (extension to OAuth)
+```
+
+### Note on PKCE
+The `code_verifier` parameter currently being sent is NOT part of the IndieAuth specification. IndieAuth does not mention PKCE (RFC 7636) support. However:
+- Including it shouldn't break compliant providers (they should ignore unknown parameters)
+- It provides additional security for public clients
+- Consider making PKCE optional or detecting provider support
+
+## Alternatives Considered
+
+### Alternative 1: Argue for Optional grant_type
+**Rejected**: While IndieAuth could theoretically make grant_type optional since there's only one grant type, this would break compatibility with OAuth 2.0 compliant libraries and providers.
+
+### Alternative 2: Provider-specific workarounds
+**Rejected**: Creating provider-specific code paths would violate the principle of standards compliance and create maintenance burden.
+
+## Recommendation
+
+**Immediate Action Required**:
+1. Add `grant_type=authorization_code` to all token exchange requests
+2. Maintain the existing parameters
+3. Consider making PKCE optional or auto-detecting provider support
+
+**StarPunk is at fault** - the implementation is missing a required OAuth 2.0 parameter that IndieAuth inherits.
+
+## References
+- [OAuth 2.0 RFC 6749 Section 4.1.3](https://datatracker.ietf.org/doc/html/rfc6749#section-4.1.3)
+- [IndieAuth W3C TR Section 6.3.1](https://www.w3.org/TR/indieauth/#token-request)
+- [PKCE RFC 7636](https://datatracker.ietf.org/doc/html/rfc7636) (not part of IndieAuth spec)

docs/reports/2025-11-22-authorization-endpoint-fix.md

@@ -0,0 +1,93 @@
+# IndieAuth Authentication Endpoint Correction
+
+**Date**: 2025-11-22
+**Version**: 0.9.4
+**Type**: Bug Fix
+
+## Summary
+
+Corrected the IndieAuth code redemption endpoint from `/token` to `/authorize` for authentication-only flows, and removed the unnecessary `grant_type` parameter.
+
+## Problem
+
+StarPunk was using the wrong endpoint for IndieAuth authentication. Per the IndieAuth specification:
+
+- **Authentication-only flows** (identity verification): Use the **authorization endpoint** (`/authorize`)
+- **Authorization flows** (getting access tokens): Use the **token endpoint** (`/token`)
+
+StarPunk only needs identity verification (to check if the user is the admin), so it should POST to the authorization endpoint, not the token endpoint.
+
+Additionally, the `grant_type` parameter is only required for token endpoint requests (OAuth 2.0 access token requests), not for authentication-only code redemption at the authorization endpoint.
+
+### IndieAuth Spec Reference
+
+From the IndieAuth specification:
+> If the client only needs to know the user who logged in, the client will exchange the authorization code at the authorization endpoint. If the client needs an access token, the client will exchange the authorization code at the token endpoint.
+
+## Solution
+
+1. Changed the endpoint from `/token` to `/authorize`
+2. Removed the `grant_type` parameter (not needed for authentication-only)
+3. Updated debug logging to reflect "code verification" instead of "token exchange"
+
+### Before
+
+```python
+token_exchange_data = {
+    "grant_type": "authorization_code",  # Not needed for authentication-only
+    "code": code,
+    "client_id": current_app.config["SITE_URL"],
+    "redirect_uri": f"{current_app.config['SITE_URL']}auth/callback",
+    "code_verifier": code_verifier,
+}
+
+token_url = f"{current_app.config['INDIELOGIN_URL']}/token"  # Wrong endpoint
+```
+
+### After
+
+```python
+token_exchange_data = {
+    "code": code,
+    "client_id": current_app.config["SITE_URL"],
+    "redirect_uri": f"{current_app.config['SITE_URL']}auth/callback",
+    "code_verifier": code_verifier,
+}
+
+# Use authorization endpoint for authentication-only flow (identity verification)
+token_url = f"{current_app.config['INDIELOGIN_URL']}/authorize"
+```
+
+## Files Modified
+
+1. **`starpunk/auth.py`**
+   - Line 410-423: Removed `grant_type`, changed endpoint to `/authorize`, added explanatory comments
+   - Line 434: Updated log message from "token exchange request" to "code verification request to authorization endpoint"
+   - Line 445: Updated comment to clarify authentication-only flow
+   - Line 455: Updated log message from "token exchange response" to "code verification response"
+
+2. **`starpunk/__init__.py`**
+   - Version bumped from 0.9.3 to 0.9.4
+
+3. **`CHANGELOG.md`**
+   - Added 0.9.4 release notes
+
+## Testing
+
+- All tests pass at the same rate as before (no new failures introduced)
+- 28 pre-existing test failures remain (related to OAuth metadata and h-app tests for removed functionality from v0.8.0)
+- 486 tests pass
+
+## Technical Context
+
+The v0.9.3 fix that added `grant_type` was based on an incorrect assumption that IndieLogin.com uses the token endpoint for all code redemption. However:
+
+1. IndieLogin.com follows the IndieAuth spec which distinguishes between authentication and authorization
+2. For authentication-only (which is all StarPunk needs), the authorization endpoint is correct
+3. The token endpoint is only for obtaining access tokens (which StarPunk doesn't need)
+
+## References
+
+- [IndieAuth Specification - Authentication](https://indieauth.spec.indieweb.org/#authentication)
+- [IndieAuth Specification - Authorization Endpoint](https://indieauth.spec.indieweb.org/#authorization-endpoint)
+- ADR-022: IndieAuth Authentication Endpoint Correction (if created)

docs/reports/2025-11-22-grant-type-fix.md

@@ -0,0 +1,68 @@
+# IndieAuth Token Exchange grant_type Fix
+
+**Date**: 2025-11-22
+**Version**: 0.9.3
+**Type**: Bug Fix
+
+## Summary
+
+Added the required `grant_type=authorization_code` parameter to the IndieAuth token exchange request.
+
+## Problem
+
+The token exchange request in `starpunk/auth.py` was missing the `grant_type` parameter. Per OAuth 2.0 spec (RFC 6749 Section 4.1.3), the token exchange request MUST include:
+
+```
+grant_type=authorization_code
+```
+
+Some IndieAuth providers that strictly validate OAuth 2.0 compliance would reject the token exchange request without this parameter.
+
+## Solution
+
+Added `"grant_type": "authorization_code"` to the `token_exchange_data` dictionary in the `handle_callback` function.
+
+### Before
+
+```python
+token_exchange_data = {
+    "code": code,
+    "client_id": current_app.config["SITE_URL"],
+    "redirect_uri": f"{current_app.config['SITE_URL']}auth/callback",
+    "code_verifier": code_verifier,
+}
+```
+
+### After
+
+```python
+token_exchange_data = {
+    "grant_type": "authorization_code",
+    "code": code,
+    "client_id": current_app.config["SITE_URL"],
+    "redirect_uri": f"{current_app.config['SITE_URL']}auth/callback",
+    "code_verifier": code_verifier,
+}
+```
+
+## Files Modified
+
+1. **`starpunk/auth.py`** (line 412)
+   - Added `"grant_type": "authorization_code"` to token_exchange_data
+
+2. **`starpunk/__init__.py`** (line 156)
+   - Version bumped from 0.9.2 to 0.9.3
+
+3. **`CHANGELOG.md`**
+   - Added 0.9.3 release notes
+
+## Testing
+
+- Module imports successfully
+- Pre-existing test failures are unrelated (OAuth metadata and h-app tests for removed functionality)
+- No new test failures introduced
+
+## References
+
+- RFC 6749 Section 4.1.3: Access Token Request
+- IndieAuth specification

starpunk/__init__.py

@@ -153,5 +153,5 @@ def create_app(config=None):
 
 # Package version (Semantic Versioning 2.0.0)
 # See docs/standards/versioning-strategy.md for details
-__version__ = "0.9.2"
-__version_info__ = (0, 9, 2)
+__version__ = "0.9.4"
+__version_info__ = (0, 9, 4)

starpunk/auth.py

@@ -407,7 +407,11 @@ def handle_callback(code: str, state: str, iss: Optional[str] = None) -> Optiona
 
     current_app.logger.debug(f"Auth: Issuer verified: {iss}")
 
-    # Prepare token exchange request with PKCE verifier
+    # Prepare code verification request with PKCE verifier
+    # Note: For authentication-only flows (identity verification), we use the
+    # authorization endpoint, not the token endpoint. grant_type is not needed.
+    # See IndieAuth spec: authorization endpoint for authentication,
+    # token endpoint for access tokens.
     token_exchange_data = {
         "code": code,
         "client_id": current_app.config["SITE_URL"],
@@ -415,7 +419,8 @@ def handle_callback(code: str, state: str, iss: Optional[str] = None) -> Optiona
         "code_verifier": code_verifier,  # PKCE verification
     }
 
-    token_url = f"{current_app.config['INDIELOGIN_URL']}/token"
+    # Use authorization endpoint for authentication-only flow (identity verification)
+    token_url = f"{current_app.config['INDIELOGIN_URL']}/authorize"
 
     # Log the request (code_verifier will be redacted)
     _log_http_request(
@@ -426,7 +431,7 @@ def handle_callback(code: str, state: str, iss: Optional[str] = None) -> Optiona
 
     # Log detailed httpx request info for debugging
     current_app.logger.debug(
-        "Auth: Sending token exchange request:\n"
+        "Auth: Sending code verification request to authorization endpoint:\n"
         "  Method: POST\n"
         "  URL: %s\n"
         "  Data: code=%s, client_id=%s, redirect_uri=%s, code_verifier=%s",
@@ -437,7 +442,7 @@ def handle_callback(code: str, state: str, iss: Optional[str] = None) -> Optiona
         _redact_token(code_verifier),
     )
 
-    # Exchange code for identity (CORRECT ENDPOINT: /token)
+    # Exchange code for identity at authorization endpoint (authentication-only flow)
     try:
         response = httpx.post(
             token_url,
@@ -447,7 +452,7 @@ def handle_callback(code: str, state: str, iss: Optional[str] = None) -> Optiona
 
         # Log detailed httpx response info for debugging
         current_app.logger.debug(
-            "Auth: Received token exchange response:\n"
+            "Auth: Received code verification response:\n"
             "  Status: %d\n"
             "  Headers: %s\n"
             "  Body: %s",