Why does my file upload from Blazor WebApp directly to AWS/MinIO close the connection?

I'm currently trying to create an Aspire based project where, among other things, you can upload files to a MinIO backend. In order to somewhat minimize the shoving around of files, I'm trying to upload user files directly from the Web Client to MinIO.

The flow is as follows:

1. The Blazor Client gets a presigned MinIO url for upload in order to not expose the credentials for the bucket
2. The user selects a file and the Blazor Client reads it as a StreamContent.
3. The HttpClient then PUTs the file as a stream to the MinIO instance

The presigned MinIO url works and I can upload files using Postman just fine. Reading the file also works. It's when it comes to step 3 that things go wrong. I'm always getting an exception like this:

System.Net.Http.HttpRequestException: Error while copying content to a stream. ---> System.IO.IOException: Unable to write data to the transport connection: An existing connection was closed by the remote host..

This is the code in question:

@page "/fileupload"@using System.Linq@using System.Net.Http.Headers@inject MinIOClient client@inject ILogger<FileUpload> Logger@inject HttpClient httpClient@rendermode InteractiveServer<PageTitle>File Upload 2</PageTitle><h1>File Upload Example 2</h1><p><label>        Upload <InputFile OnChange="OnInputFileChange" /></label></p>@if (file != null){<div class="card"><div class="card-body"><ul><li>                    File: @file.Name<br>                    @if (FileUploadResults(uploadResult, file.Name, Logger, out var result))                    {<span>                            Stored File Name: @result.StoredFileName</span>                    }                    else                    {<span>                            There was an error uploading the file (Error: @result.ErrorCode).</span>                    }</li></ul></div></div>}@code {    private File? file;    private UploadResult uploadResult = new();    private bool shouldRender;    string url = string.Empty;    protected override bool ShouldRender() => shouldRender;    private async Task OnInputFileChange(InputFileChangeEventArgs e)    {        shouldRender = false;        long maxFileSize = 1024 * 1024 * 1024;        var selectedFile = e.File;        if (selectedFile != null)        {            try            {                file = new() { Name = selectedFile.Name };                //This gets the presigned MinIO url                var resp = await client.GetUrl();                if (resp is null) return;                using var content = new MultipartFormDataContent();                var fileContent = new StreamContent(selectedFile.OpenReadStream(maxFileSize));                fileContent.Headers.ContentType = new MediaTypeHeaderValue(selectedFile.ContentType);                content.Add(content: fileContent, name: "\"file\"", fileName: selectedFile.Name);                var response = await httpClient.PutAsync(resp, content);                // Assuming the response contains the upload result                // Update the uploadResult based on the response                // For example:                // uploadResult = await response.Content.ReadFromJsonAsync<UploadResult>();                // Simulate a successful upload result for demonstration                uploadResult = new UploadResult                    {                        FileName = selectedFile.Name,                        StoredFileName = "stored_" + selectedFile.Name,                        Uploaded = true                    };            }            catch (Exception ex)            {                Logger.LogInformation("{FileName} not uploaded (Err: 6): {Message}", selectedFile.Name, ex.Message);                uploadResult = new UploadResult                    {                        FileName = selectedFile.Name,                        ErrorCode = 6,                        Uploaded = false                    };            }        }        shouldRender = true;    }    private static bool FileUploadResults(UploadResult uploadResult, string? fileName, ILogger<FileUpload> logger, out UploadResult result)    {        result = uploadResult;        if (!result.Uploaded)        {            logger.LogInformation("{FileName} not uploaded (Err: 5)", fileName);            result.ErrorCode = 5;        }        return result.Uploaded;    }    private class File    {        public string? Name { get; set; }    }    private class UploadResult    {        public string? FileName { get; set; }        public string? StoredFileName { get; set; }        public bool Uploaded { get; set; }        public int ErrorCode { get; set; }    }}

Already tried several variants but they all yield the same error...