rust-s3: Signature mismatch

Describe the bug

When using bucket.presign_get("/some/path/file.txt"), I get a signature mismatch with some DigitalOcean spaces. The generated presigned URL always contains the slashes in the path encoded as %2F, and sometimes this is okay (changing them to /es does not break the presigned URL), but sometimes I get a signature mismatch (changing them to /es then fixes the presigned URL). I’m not sure whether percent-encoding the path before signing would help, or just make it fail with other servers. Another approach would be to never percent-encode slashes, which all servers seem to support according to the analysis in #133.

To Reproduce

I’ve uploaded an empty file to the S3 space that has this issue. The following presigned URL is valid for 7 days:

https://lumeo-api.sfo2.digitaloceanspaces.com/s3-signing-issue/foo.txt?X-Amz-Algorithm=AWS4-HMAC-SHA256&X-Amz-Credential=LGYCZBSFXVLMQBZMXVBB%2F20201201%2Fsfo2%2Fs3%2Faws4_request&X-Amz-Date=20201201T114438Z&X-Amz-Expires=604800&X-Amz-SignedHeaders=host&X-Amz-Signature=9ee914bd679aed482b05849bf615a9f8bb39f13ceefd0618c0b014647b78e0db

Here is the same URL, with the / before foo.txt encoded as %2F. You get a signature mismatch when requesting it:

https://lumeo-api.sfo2.digitaloceanspaces.com/s3-signing-issue%2Ffoo.txt?X-Amz-Algorithm=AWS4-HMAC-SHA256&X-Amz-Credential=LGYCZBSFXVLMQBZMXVBB%2F20201201%2Fsfo2%2Fs3%2Faws4_request&X-Amz-Date=20201201T114438Z&X-Amz-Expires=604800&X-Amz-SignedHeaders=host&X-Amz-Signature=9ee914bd679aed482b05849bf615a9f8bb39f13ceefd0618c0b014647b78e0db

Expected behavior

The URL generated by .presign_get should work…

Environment

• Rust version: 1.48.0
• lib version 0.26.3