UserServiceWithAuthenticationHandler.cs

public class UserService : 
{
    private readonly HttpClient _httpClient;
    public UserService(HttpClient httpClient)
    {
        _httpClient = httpClient;
    }

    public async Task<IReadOnlyCollection<User>> GetAllUsers()
    {
        var response = await _httpClient.GetAsync(new Uri("user"));
        response.EnsureSuccessStatusCode();
        return await response.Content.ReadAsAsync<IReadOnlyCollection<User>>();
    }

    public async Task UpdateUser(User userToUpdate)
    {
        var content = new StringContent(JsonConvert.SerializeObject(userToUpdate));
        var response = await _httpClient.PutAsync($"user/{userToUpdate.Name}", content);
        response.EnsureSuccessStatusCode();
    }
}