I known swift3 only support signature v2. And the V4 isn't implement. Maybe we should put it on our blueprint.
Test with s3cmd v1.5.0 and it return a 412 Error.
$ s3cmd --debug ls s3://test3
DEBUG: ConfigParser: Reading file '/Users/charles/.s3cfg'
DEBUG: ConfigParser: access_key->te...8_chars...r
DEBUG: ConfigParser: access_token->
DEBUG: ConfigParser: add_encoding_exts->
DEBUG: ConfigParser: add_headers->
DEBUG: ConfigParser: bucket_location->US
DEBUG: ConfigParser: cache_file->
DEBUG: ConfigParser: cloudfront_host->192.168.200.201
DEBUG: ConfigParser: default_mime_type->binary/octet-stream
DEBUG: ConfigParser: delay_updates->False
DEBUG: ConfigParser: delete_after->False
DEBUG: ConfigParser: delete_after_fetch->False
DEBUG: ConfigParser: delete_removed->False
DEBUG: ConfigParser: dry_run->False
DEBUG: ConfigParser: enable_multipart->True
DEBUG: ConfigParser: encoding->UTF-8
DEBUG: ConfigParser: encrypt->False
DEBUG: ConfigParser: follow_symlinks->False
DEBUG: ConfigParser: force->False
DEBUG: ConfigParser: get_continue->False
DEBUG: ConfigParser: gpg_command->None
DEBUG: ConfigParser: gpg_decrypt->%(gpg_command)s -d --verbose --no-use-agent --batch --yes --passphrase-fd %(passphrase_fd)s -o %(output_file)s %(input_file)s
DEBUG: ConfigParser: gpg_encrypt->%(gpg_command)s -c --verbose --no-use-agent --batch --yes --passphrase-fd %(passphrase_fd)s -o %(output_file)s %(input_file)s
DEBUG: ConfigParser: gpg_passphrase->...-3_chars...
DEBUG: ConfigParser: guess_mime_type->True
DEBUG: ConfigParser: host_base->192.168.200.201
DEBUG: ConfigParser: host_bucket->192.168.200.201
DEBUG: ConfigParser: human_readable_sizes->False
DEBUG: ConfigParser: invalidate_default_index_on_cf->False
DEBUG: ConfigParser: invalidate_default_index_root_on_cf->True
DEBUG: ConfigParser: invalidate_on_cf->False
DEBUG: ConfigParser: list_md5->False
DEBUG: ConfigParser: log_target_prefix->
DEBUG: ConfigParser: mime_type->
DEBUG: ConfigParser: multipart_chunk_size_mb->15
DEBUG: ConfigParser: preserve_attrs->True
DEBUG: ConfigParser: progress_meter->True
DEBUG: ConfigParser: proxy_host->
DEBUG: ConfigParser: proxy_port->0
DEBUG: ConfigParser: recursive->False
DEBUG: ConfigParser: recv_chunk->4096
DEBUG: ConfigParser: reduced_redundancy->False
DEBUG: ConfigParser: secret_key->te...4_chars...g
DEBUG: ConfigParser: send_chunk->4096
DEBUG: ConfigParser: simpledb_host->
DEBUG: ConfigParser: skip_existing->False
DEBUG: ConfigParser: socket_timeout->300
DEBUG: ConfigParser: urlencoding_mode->normal
DEBUG: ConfigParser: use_https->False
DEBUG: ConfigParser: verbosity->WARNING
DEBUG: ConfigParser: website_error->
DEBUG: ConfigParser: website_index->index.html
DEBUG: Updating Config.Config cache_file ->
DEBUG: Updating Config.Config follow_symlinks -> False
DEBUG: Updating Config.Config verbosity -> 10
DEBUG: Unicodising 'ls' using UTF-8
DEBUG: Unicodising 's3://test3' using UTF-8
DEBUG: Command: ls
DEBUG: Bucket 's3://test3':
DEBUG: CreateRequest: resource[uri]=/
DEBUG: Using signature v4
DEBUG: get_hostname(test3): 192.168.200.201
DEBUG: Canonical Request:
GET
/
delimiter=%2F
host:192.168.200.201
x-amz-content-sha256:e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855
x-amz-date:20150114T103925Z
host;x-amz-content-sha256;x-amz-date
e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855
----------------------
DEBUG: signature-v4 headers: {'x-amz-content-sha256': 'e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855', 'Authorization': 'AWS4-HMAC-SHA256 Credential=test:tester/20150114/US/s3/aws4_request,SignedHeaders=host;x-amz-content-sha256;x-amz-date,Signature=08293376d0c91348cfc11536a3b969d06f19477338e7258a8d81ad4f1dc882d3', 'x-amz-date': '20150114T103925Z'}
DEBUG: Processing request, please wait...
DEBUG: get_hostname(test3): 192.168.200.201
DEBUG: ConnMan.get(): creating new connection: http://192.168.200.201
DEBUG: non-proxied HTTPConnection(192.168.200.201)
DEBUG: format_uri(): /test3/?delimiter=/
DEBUG: Sending request method_string='GET', uri='/test3/?delimiter=/', headers={'x-amz-content-sha256': 'e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855', 'Authorization': 'AWS4-HMAC-SHA256 Credential=test:tester/20150114/US/s3/aws4_request,SignedHeaders=host;x-amz-content-sha256;x-amz-date,Signature=08293376d0c91348cfc11536a3b969d06f19477338e7258a8d81ad4f1dc882d3', 'x-amz-date': '20150114T103925Z'}, body=(0 bytes)
DEBUG: Response: {'status': 412, 'headers': {'date': 'Wed, 14 Jan 2015 10:39:25 GMT', 'content-length': '7', 'content-type': 'text/html; charset=UTF-8', 'x-trans-id': 'tx2ca6e281156a4fdb9bfc2-0054b6475d'}, 'reason': 'Precondition Failed', 'data': 'Bad URL'}
DEBUG: ConnMan.put(): connection put back to pool (http://192.168.200.201#1)
DEBUG: S3Error: 412 (Precondition Failed)
DEBUG: HttpHeader: date: Wed, 14 Jan 2015 10:39:25 GMT
DEBUG: HttpHeader: content-length: 7
DEBUG: HttpHeader: content-type: text/html; charset=UTF-8
DEBUG: HttpHeader: x-trans-id: tx2ca6e281156a4fdb9bfc2-0054b6475d
ERROR: Error parsing xml: syntax error: line 1, column 0
ERROR: Bad URL
DEBUG: Not an XML response
ERROR: S3 error: 412 (Precondition Failed):
or we should add something likes this.
http://