s3: support STREAMING-AWS4-HMAC-SHA256-PAYLOAD-TRAILER for signed chunked uploads with checksums (#7623)

* s3: support STREAMING-AWS4-HMAC-SHA256-PAYLOAD-TRAILER for signed chunked uploads with checksums

When AWS SDK v2 clients upload with both chunked encoding and checksum
validation enabled, they use the x-amz-content-sha256 header value of
STREAMING-AWS4-HMAC-SHA256-PAYLOAD-TRAILER instead of the simpler
STREAMING-AWS4-HMAC-SHA256-PAYLOAD.

This caused the chunked reader to not be properly activated, resulting
in chunk-signature metadata being stored as part of the file content.

Changes:
- Add streamingSignedPayloadTrailer constant for the new header value
- Update isRequestSignStreamingV4() to recognize this header
- Update newChunkedReader() to handle this streaming type
- Update calculateSeedSignature() to accept this header
- Add unit test for signed streaming upload with trailer

Fixes issue where Quarkus/AWS SDK v2 uploads with checksum validation
resulted in corrupted file content containing chunk-signature data.

* address review comments: add trailer signature to test, fix constant alignment

* test: separate canonical trailer text (\n) from on-wire format (\r\n)

* test: add negative test for invalid trailer signature

* refactor: check HTTP method first in streaming auth checks (fail-fast)

* test: handle crc32 Write error return for completeness

* refactor: extract createTrailerStreamingRequest helper to reduce test duplication

* fmt

* docs: clarify test comment about trailer signature validation status

* refactor: calculate chunk data length dynamically instead of hardcoding

* Update weed/s3api/chunked_reader_v4_test.go

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

* fix: use current time for signatures instead of hardcoded past date

---------

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

weed/s3api/s3api_auth.go

@@ -48,14 +48,22 @@ func isRequestPostPolicySignatureV4(r *http.Request) bool {
 }
 
 // Verify if the request has AWS Streaming Signature Version '4'. This is only valid for 'PUT' operation.
+// Supports both with and without trailer variants:
+// - STREAMING-AWS4-HMAC-SHA256-PAYLOAD (original)
+// - STREAMING-AWS4-HMAC-SHA256-PAYLOAD-TRAILER (with trailing checksums)
 func isRequestSignStreamingV4(r *http.Request) bool {
-	return r.Header.Get("x-amz-content-sha256") == streamingContentSHA256 &&
-		r.Method == http.MethodPut
+	if r.Method != http.MethodPut {
+		return false
+	}
+	contentSha256 := r.Header.Get("x-amz-content-sha256")
+	return contentSha256 == streamingContentSHA256 || contentSha256 == streamingContentSHA256Trailer
 }
 
 func isRequestUnsignedStreaming(r *http.Request) bool {
-	return r.Header.Get("x-amz-content-sha256") == streamingUnsignedPayload &&
-		r.Method == http.MethodPut
+	if r.Method != http.MethodPut {
+		return false
+	}
+	return r.Header.Get("x-amz-content-sha256") == streamingUnsignedPayload
 }
 
 // Authorization type.