Add POST /api/upload-file endpoint that uploads files to S3 and returns
CDN URLs protected by CloudFront signed cookies (same pattern as Linear).
Infrastructure:
- Two private S3 buckets (static.multica.ai, static-staging.multica.ai)
- Two CloudFront distributions with OAC and Trusted Key Groups
- ACM wildcard cert in us-east-1, DNS records in Route 53
- RSA signing key stored in AWS Secrets Manager
Backend:
- S3 storage service with CloudFront CDN domain support
- CloudFront signed cookie generation (RSA-SHA1)
- Private key loaded from Secrets Manager (env var fallback for local dev)
- Cookies set on login (VerifyCode) with 72h expiry matching JWT
- Upload handler: multipart form → S3 → CloudFront URL response
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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