CreatePresignedPostAsync appends a trailing slash to x-amz-credential, breaks SigV4 on S3-compatible servers

[Berreip]

Describe the bug

AmazonS3Client.CreatePresignedPostAsync generates x-amz-credential as:
<AccessKey>/<YYYYMMDD>/<region>/s3/aws4_request/
AWS docs define the scope without a trailing slash. Example: …/aws4_request only. Strict S3-compatible services (like Minio) reject the extra / during SigV4 parsing.
AWS Documentation POST

Code reference
File: sdk/src/Services/S3/Custom/Util/S3PostUploadSignedPolicy.cs S3PostUploadSignedPolicy.cs
Line 123:

var credentialString = string.Format(CultureInfo.InvariantCulture, "{0}/{1}/{2}/{3}/{4}/", iCreds.AccessKey, dateStamp, region, "s3", Runtime.Internal.Auth.AWS4Signer.Terminator); 

Regression Issue

• Select this option if this issue appears to be a regression.

Expected Behavior

x-amz-credential follows AWS SigV4 scope format: YYYYMMDD/region/service/aws4_request (no trailing slash).
aws reference_sigv-signing-elements

Current Behavior

x-amz-credential includes a trailing slash.

Reproduction Steps

1. Build a CreatePresignedPostRequest and call CreatePresignedPostAsync.
2. POST the returned form to a SigV4-strict S3-compatible server.
3. Receive AuthorizationQueryParametersError about date parsing. Logged fields show x-amz-credential ends with /.

Possible Solution

Emit x-amz-credential without the trailing slash, or provide an option to do so, to match AWS documentation and improve interoperability.

Additional Information/Context

No response

AWS .NET SDK and/or Package version used

AWSSDK.S3 4.0.7.13

Targeted .NET Platform

.Net Core 9

Operating System and version

Windows 11

[GarrettBeatty]

i checked the java sdk and it seems like doesnt end with slash. https://github.com/aws/aws-sdk-java-v2/blob/81f33e06e9a328721d4b5def35cf8f84cfde1762/core/http-auth-aws/src/main/java/software/amazon/awssdk/http/auth/aws/internal/signer/CredentialScope.java#L61.

will chat with team on priority of this issue