var fileProvider = new S3FileProvider(amazonS3Service, bucketName);

public void Configure(IApplicationBuilder app)
{
    // ...
    
    var fileProvider = new S3FileProvider(amazonS3, "bucket-name");

    var staticFilesOption = new StaticFileOptions()
    {
        FileProvider = fileProvider
    };
    app.UseStaticFiles(staticFilesOption);
    
    // ...
}

var amazonS3 = new Amazon.S3.AmazonS3Client("awsAccessKeyId", "awsSecretAccessKey", Amazon.RegionEndpoint.USWest2);

var amazonS3 = app.ApplicationServices.GetService<Amazon.S3.IAmazonS3>();