Currenty I building a solution which is basically an integration between multiple external REST services. Since the solution is having multiple external service, I want to use the .NET ClientFactory to create HttpClients whenever they are wanted. Unfortunately an HttpClient instance created from the ClientFactory always results in an Unauthorized. This is a bit strange since directly creating a new HttpClient results in a success. I red the Microsoft documentation about the HttpClientFactory to determine the differences and possible use cases.

I compared the two different HttpClient instances by extracting the entire objects and did a meld comparison without any differences. Also with postman the call to the service succeeds.

The code which extracts and creates the HttpClient instance (which fails) looks like this:

Programm.cs

 ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls12;

 services.AddHttpClient("ClientName", client =>
 {
     client.BaseAddress = new Uri("https://my.domain.com");
     var credentials = Convert.ToBase64String(Encoding.UTF8.GetBytes("username:password"));
     client.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue("Basic", credentials);
     // Set the content type header
     client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));
 });

TicketRepository.cs

public class TicketsRepository(
    IHttpClientFactory _httpClientFactory) : ITicketsRepository
{
    private readonly HttpClient _httpClient = _httpClientFactory.CreateClient("ClientName");

    public async Task<Tickets> GetTicketByNumber(
        int ticket,
        CancellationToken cancellationToken)
    {
        // HttpContent content = new StringContent(string.Empty);
        HttpResponseMessage response = await _httpClient.GetAsync(
            $"{Constants.TicketsUrlTemplate}/{ticket}",
            cancellationToken);

        if (!response.IsSuccessStatusCode)
        {
            //_logger.LogError("Could not successfully retrieve data. Invalid response data is: {response}", response.ToString());

            throw new HttpRequestException($"PhpServer dit not respond with an http response status 200: {response}");
        }

        return new Tickets();
    }
}

The code which creates an HttpClient instance on every method call and succeeds extracting data looks like this:

public async Task GetTicketByNumber(
    int ticket,
    CancellationToken cancellationToken)
{
    using (HttpClient client = new HttpClient())
    {
            Set the base address
        client.BaseAddress = new Uri("https://my.domain.com");

            Set the basic authentication header
        var credentials = Convert.ToBase64String(Encoding.UTF8.GetBytes("username:password"));
        client.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue("Basic", credentials);

            Set the content type header
        client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));

        try
        {
                Make the GET request
            HttpResponseMessage response = await client.GetAsync($"/urlTemplate/{ticket}/", cancellationToken);

                Check for success
            response.EnsureSuccessStatusCode();

                Read and log the response content
            string responseContent = await response.Content.ReadAsStringAsync();
            Console.WriteLine("Response Content: " + responseContent);
        }
        catch (HttpRequestException e)
        {
            Console.WriteLine("Request error: " + e.Message);
        }
    }
}

I did a blank comparison with the Response Objects and HttpClient Objects with identical headers, version, host etc… I must have overlooked something stupid since the ClientFactory works for other Rest Services configured on startup. It is hard to monitor stuf on the server side, since I do not have any physical acccess towards that REST Service, nor do I have access to the source of it. Hopefully someone can point me in the right direction.