C# HaveIBeenPwned

PasswordPwnedService.cs

using System;
using System.Linq;
using System.Net.Http;
using System.Security.Cryptography;
using System.Text;
using System.Threading.Tasks;

namespace McCauley.Util.Services
{
	public interface IPasswordPwnedService
	{
		Task<bool> IsPasswordPwned(string password);
	}
	public class PasswordPwnedService : IPasswordPwnedService
	{
		private readonly HttpClient httpClient;

		public PasswordPwnedService(HttpClient httpClient)
		{
			this.httpClient = httpClient;
		}

		public async Task<bool> IsPasswordPwned(string password)
		{
			var isPwned = false;
			var hash = new SHA1Managed().ComputeHash(Encoding.UTF8.GetBytes(password));
			var hashString = string.Concat(hash.Select(b => b.ToString("X2")));
			var firstPart = hashString.Substring(0, 5);
			var secondPart = hashString.Substring(5);
			var response = await httpClient.GetAsync($"https://api.pwnedpasswords.com/range/{firstPart}");
			if (response.IsSuccessStatusCode)
			{
				var responseBody = await response.Content.ReadAsStringAsync();
				isPwned = responseBody.Split(Environment.NewLine).Any(row => row.StartsWith(secondPart));
			}
			return isPwned;
		}
	}
}