fix s3 requests sent to outpost arn missing x-amz-content-sha256 head…

…er (#4857)

CHANGELOG_PENDING.md

@@ -3,3 +3,6 @@
 ### SDK Enhancements
 
 ### SDK Bugs
+
+* `service/s3`: Populate X-Amz-Content-Sha256 header when using s3 outpost arn
+  * Using an outpost ARN results in a different signing name from the resolved endpoint. This signing name was not included in the signer logic to indicate the `X-Amz-Content-Sha256` header should be added to the request which is required by S3.

aws/signer/v4/v4.go

@@ -3,7 +3,7 @@
 // Provides request signing for request that need to be signed with
 // AWS V4 Signatures.
 //
-// Standalone Signer
+// # Standalone Signer
 //
 // Generally using the signer outside of the SDK should not require any additional
 // logic when using Go v1.5 or higher. The signer does this by taking advantage
@@ -14,10 +14,10 @@
 // The signer will first check the URL.Opaque field, and use its value if set.
 // The signer does require the URL.Opaque field to be set in the form of:
 //
-//     "//<hostname>/<path>"
+//	"//<hostname>/<path>"
 //
-//     // e.g.
-//     "//example.com/some/path"
+//	// e.g.
+//	"//example.com/some/path"
 //
 // The leading "//" and hostname are required or the URL.Opaque escaping will
 // not work correctly.
@@ -695,7 +695,8 @@ func (ctx *signingCtx) buildBodyDigest() error {
 		includeSHA256Header := ctx.unsignedPayload ||
 			ctx.ServiceName == "s3" ||
 			ctx.ServiceName == "s3-object-lambda" ||
-			ctx.ServiceName == "glacier"
+			ctx.ServiceName == "glacier" ||
+			ctx.ServiceName == "s3-outposts"
 
 		s3Presign := ctx.isPresign &&
 			(ctx.ServiceName == "s3" ||