`GetPreSignedURLAsync` returns real AWS URL instead of localstack one

[julealgon]

🐛 Bug Description

What happened?
After configuring localstack and injecting IAmazonS3 into my service, then calling GetPreSignedURLAsync on the client, the returned URL points to the real http://s3.us-east-1.amazonaws.com/test-bucket/... instead of my locally running http://localhost:64847/test-bucket/... container instance.

For whatever reason, this only seems to affect the presign method: all other operations interact with my emulator just fine.

I can also see that the client has proper proxy settings in it so it is picking up the configuration as expected:

• ProxyPort: 64847
• ProxyHost: "localhost"

What did you expect to happen?
I would expect that any presigned URLs generated with the adapted IAmazonS3 client from localstack would honor the same domain/port as the emulator instead of falling back to what seems to be the standard real AWS S3 base URL.

🔄 Steps to Reproduce

1. Setup localstack
2. Inject IAmazonS3
3. Call GetPreSignedURLAsync
4. Observe base URL points to real S3

Minimal code example:

var multipartResponse = await client.InitiateMultipartUploadAsync(
    new()
    {
        BucketName = "test-bucket",
        Key = "some-key",
    });

GetPreSignedUrlRequest presignedRequest = new()
{
    BucketName = "test-bucket",
    Key = "some-key",
    PartNumber = 1,
    UploadId = multipartResponse.UploadId,
    Verb = HttpVerb.PUT,
};

Uri presignedUrl = new(await client.GetPreSignedURLAsync(presignedRequest));

📋 Environment Information

LocalStack.Client Version:

• v1.x (AWS SDK v3) - LTS Branch
• v2.x (AWS SDK v4) - Current Branch
• Version: 2.0.0

LocalStack Information:

• LocalStack Version: 4.12.0
• LocalStack Image: docker.io/localstack/localstack:4.12.0
• LocalStack Services Used: S3

.NET Information:

• .NET Version: .NET 10
• Operating System: Windows 11
• IDE/Editor: Visual Studio 2026

AWS SDK Information:

• AWS SDK Version:
  • AWSSDK.S3 4.0.18.7
  • AWSSDK.Core 4.0.3.15
• Services: S3

🔍 Additional Context

Configuration (Optional):

// Your LocalStack configuration (appsettings.json snippet)
{
  "LocalStack": {
    "EnableLocalStack": true
  }
}

Error Messages/Stack Traces:

Paste any error messages or stack traces here

Screenshots:
If applicable, add screenshots to help explain your problem.

Additional Information:
Add any other context about the problem here.

✅ Checklist

• I have searched existing issues to ensure this is not a duplicate
• I have provided all the requested information above
• I have tested this with the latest version of LocalStack.Client
• I have verified this issue occurs with LocalStack (not with real AWS services)

[julealgon]

I've worked around this issue for now by introducing this parameter (which I found by accident while looking for something else on the same method):

-.AddAWSServiceLocalStack<IAmazonS3>()
+.AddAWSServiceLocalStack<IAmazonS3>(useServiceUrl: true)

After this, I see the same localhost and port on the generated presigned URLs.

However, I still believe it should work normally even without this.

[Blind-Striker]

Hey @julealgon ,thanks for the report 🙏 I'll look into it