Fixed the critical issues identified in GitHub PR review that were causing
JWT authentication failures in S3 IAM integration tests.
### Problem Identified:
- evaluateStringCondition function was a stub that always returned shouldMatch
- Trust policy validation was doing basic checks instead of proper evaluation
- String conditions (StringEquals, StringNotEquals, StringLike) were ignored
- JWT authentication failing with errCode=1 (AccessDenied)
### Solution Implemented:
**1. Fixed evaluateStringCondition in policy engine:**
- Implemented proper string condition evaluation with context matching
- Added support for exact matching (StringEquals/StringNotEquals)
- Added wildcard support for StringLike conditions using filepath.Match
- Proper type conversion for condition values and context values
**2. Implemented comprehensive trust policy validation:**
- Added parseJWTTokenForTrustPolicy to extract claims from web identity tokens
- Created evaluateTrustPolicy method with proper Principal matching
- Added support for Federated principals (OIDC/SAML)
- Implemented trust policy condition evaluation
- Added proper context mapping (seaweed:FederatedProvider, etc.)
**3. Enhanced IAM manager with trust policy evaluation:**
- validateTrustPolicyForWebIdentity now uses proper policy evaluation
- Extracts JWT claims and maps them to evaluation context
- Supports StringEquals, StringNotEquals, StringLike conditions
- Proper Principal matching for Federated identity providers
### Technical Details:
- Added filepath import for wildcard matching
- Added base64, json imports for JWT parsing
- Trust policies now check Principal.Federated against token idp claim
- Context values properly mapped: idp → seaweed:FederatedProvider
- Condition evaluation follows AWS IAM policy semantics
### Addresses GitHub PR Review:
This directly fixes the issue mentioned in the PR review about
evaluateStringCondition being a stub that doesn't implement actual
logic for StringEquals, StringNotEquals, and StringLike conditions.
The trust policy validation now properly enforces policy conditions,
which should resolve the JWT authentication failures.