SigV4 authenticated uploads fail with SignatureDoesNotMatch on Cloudflare Workers

Here's a more general GitHub issue:

### What I'm trying to do

I'm trying to use rclone to upload files to a multistore proxy running on Cloudflare Workers. Anonymous reads work fine, but authenticated writes (PUT) and authenticated list operations (GET with credentials) all fail with `403 SignatureDoesNotMatch`.

Has anyone gotten authenticated uploads working with the Cloudflare Workers deployment?

### My setup

**rclone config:**

```ini
[dataforcanada-s3]
type = s3
provider = Other
endpoint = https://s3.dataforcanada.org
no_check_bucket = true
access_key_id =
secret_access_key =
env_auth = false
```

**Upload command:**

```bash
rclone copy . dataforcanada-s3:dataforcanada/d4c-datapkg-orthoimagery/
```

**Wrangler config (sanitized):**

```toml
compatibility_date = "2024-11-11"
main = "build/worker/shim.mjs"
name = "dataforcanada-s3"

[build]
command = "cargo install worker-build && worker-build --release"

[vars]
VIRTUAL_HOST_DOMAIN = "s3.dataforcanada.org"

[[routes]]
pattern = "s3.dataforcanada.org"
custom_domain = true

[vars.PROXY_CONFIG]

[[vars.PROXY_CONFIG.buckets]]
allowed_roles = []
anonymous_access = true
backend_type = "s3"
backend_prefix = "dataforcanada/"
name = "dataforcanada"

[vars.PROXY_CONFIG.buckets.backend_options]
bucket_name = "us-west-2.opendata.source.coop"
endpoint = "https://s3.us-west-2.amazonaws.com"
region = "us-west-2"
access_key_id = ""
secret_access_key = ""
skip_signature = "true"

[[vars.PROXY_CONFIG.credentials]]
access_key_id = ""
created_at = "2025-01-01T00:00:00Z"
enabled = true
principal_name = "dataforcanada-admin"
secret_access_key = ""

[[vars.PROXY_CONFIG.credentials.allowed_scopes]]
actions = [
"get_object",
"head_object",
"put_object",
"delete_object",
"list_bucket",
"create_multipart_upload",
"upload_part",
"complete_multipart_upload",
"abort_multipart_upload",
]
bucket = "dataforcanada"
prefixes = []

[placement]
mode = "smart"

[observability]
enabled = true
```

### What I see

Every authenticated request fails with a SigV4 signature mismatch. From `wrangler tail`:

```
[WARN] multistore::auth::sigv4: SigV4 signature mismatch { access_key_id=, region=us-east-1 }
[WARN] multistore::proxy: request failed { error=signature mismatch, status=403, s3_code=SignatureDoesNotMatch }
```

I can provide more detailed logs if you need them.

### Question

Has anyone successfully used authenticated uploads (PutObject) with the Cloudflare Workers deployment?