## Title
fix(cors): return single matching origin instead of multiple values in `Access-Control-Allow-Origin`
## Summary
This PR fixes bucket CORS responses when a single CORS rule contains multiple `AllowedOrigins`.
Previously, Garage returned the configured origins as a comma-separated list in `Access-Control-Allow-Origin`, for example:
```http
Access-Control-Allow-Origin: https://app.example.test, https://admin.example.test
```
This is not the expected browser-facing behavior.
When a request origin matches a configured rule, the response should reflect **only the matching request origin**, unless the rule contains `*`.
## What changed
- `Access-Control-Allow-Origin` now behaves as follows:
- returns `*` when the matched rule contains a wildcard origin
- otherwise returns the request `Origin` as a **single value**
- added `Vary: Origin` when ACAO reflects the request origin
- added preflight-specific `Vary` handling in the preflight path for:
- `Origin`
- `Access-Control-Request-Method`
- `Access-Control-Request-Headers`
## Scope
This change applies to shared bucket CORS handling paths, including:
- S3 API responses
- K2V API responses
- S3 POST object responses
- web bucket responses
- preflight (`OPTIONS`) bucket CORS responses
This does **not** change admin API fixed CORS behavior.
## Reproduction
A direct repro script is included:
```bash
./script/test-cors-multi-origin.sh
```
It exercises two cases against a direct single-node Garage instance:
1. **single-origin control**
2. **multi-origin repro**
Before this fix, the multi-origin case returned a comma-separated ACAO value.
After this fix, both cases reflect only the request origin.
## Example behavior
### Before
```http
Access-Control-Allow-Origin: https://app.example.test, https://admin.example.test
```
### After
```http
Access-Control-Allow-Origin: https://app.example.test
```
## Tests
Added/updated tests in `src/api/common/cors.rs` for:
- single-origin control
- multiple allowed origins reflecting the request origin
- wildcard origin preserving `*`
- preserving existing `Vary` values while appending `Origin`
## Validation
Used for validation:
```bash
cargo test -p garage_api_common cors::tests -- --nocapture
cargo build -p garage --bin garage
./script/test-cors-multi-origin.sh
```
## Reproducibility
For reviewers who want to validate behavior by commit:
- Before fix: `aa368e4b`
- includes the direct repro script and the regression test setup
- multi-origin ACAO is reproduced as a comma-separated value
- After fix: `f630eb92`
- reflects only the matching request origin
- preserves wildcard behavior
- adds `Vary: Origin` and preflight-specific `Vary` handling
Branch:
- `fix/cors-multiple-allow-origin`
Base used during validation:
- `74ad3bf8` (`main-v2`)
ClosesDeuxfleurs/garage#1149
Reviewed-on: https://git.deuxfleurs.fr/Deuxfleurs/garage/pulls/1419
and use workspace configuration in each package.
This allow to customize clippy and rust lint configuration for project.
No particular configuration in this commit.
Minkyu Kim