shoc-backend/SeaHavenIndustries.Tests/PasswordResetAbuseLimitsTests.cs

using System.Net;
using Api.SeaHavenIndustries.Controllers;
using Api.SeaHavenIndustries.HostedServices;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;
using SeaHaven.Services.Helpers;
using SeaHaven.Services.Interfaces;

namespace SeaHavenIndustries.Tests;

/// <summary>
/// Limits that hold per account rather than per client address, the email send
/// being off the request path, and the keyed code hash.
/// </summary>
public sealed class PasswordResetAbuseLimitsTests
{
    private const string Alice = "alice@example.com";
    private const string OldPassword = "Old@12345";
    private const string NewPassword = "New@67890";
    private const string CodeNotMatched = "{\"status\":\"Error\",\"message\":\"Code Not Matched\"}";
    private const string ResetFailed = "{\"status\":\"Error\",\"message\":\"Your email or code not found please check\"}";

    private static int _nextClient;

    // A fresh client address per request, so the per-IP limit never masks the per-account one.
    private static string NextClient()
    {
        var n = Interlocked.Increment(ref _nextClient);
        return $"198.51.{n / 250 % 250}.{n % 250 + 1}";
    }

    [Fact]
    public async Task Code_requests_are_capped_per_email_at_three_an_hour_and_ten_a_day()
    {
        await using var host = await PasswordResetTestHost.StartAsync();
        await host.AddUserAsync(Alice, OldPassword);

        var responses = new List<string>();
        for (var request = 0; request < 3; request++)
            responses.Add(await (await host.ForgetPasswordAsync(Alice, NextClient())).Content.ReadAsStringAsync());
        var liveCode = host.Sent.LatestCodeFor(Alice);

        // A differently cased and padded address is the same account.
        responses.Add(await (await host.ForgetPasswordAsync("  ALICE@Example.com ", NextClient())).Content.ReadAsStringAsync());

        Assert.Equal(3, host.Sent.Messages.Count);
        Assert.Single(responses.Distinct());
        // The refused request neither sent a code nor replaced the one already sent.
        Assert.Equal(HttpStatusCode.OK, (await host.VerifyAsync(Alice, liveCode, NextClient())).StatusCode);

        for (var hour = 1; hour <= 3; hour++)
        {
            host.Time.Advance(TimeSpan.FromHours(1));
            for (var request = 0; request < 3; request++)
                await host.ForgetPasswordAsync(Alice, NextClient());
        }

        Assert.Equal(10, host.Sent.Messages.Count);

        host.Time.Advance(TimeSpan.FromHours(20));
        await host.ForgetPasswordAsync(Alice, NextClient());
        Assert.Equal(10, host.Sent.Messages.Count);

        host.Time.Advance(TimeSpan.FromHours(1));
        await host.ForgetPasswordAsync(Alice, NextClient());
        Assert.Equal(11, host.Sent.Messages.Count);
    }

    [Fact]
    public async Task Failed_checks_are_capped_per_account_across_every_code_it_is_sent()
    {
        await using var host = await PasswordResetTestHost.StartAsync();
        await host.AddUserAsync(Alice, OldPassword);

        for (var round = 0; round < 2; round++)
        {
            await host.ForgetPasswordAsync(Alice, NextClient());
            var code = host.Sent.LatestCodeFor(Alice);
            for (var attempt = 0; attempt < 5; attempt++)
                await host.VerifyAsync(Alice, WrongCode(code), NextClient());
        }

        await host.ForgetPasswordAsync(Alice, NextClient());
        var third = host.Sent.LatestCodeFor(Alice);

        Assert.Equal(CodeNotMatched, await (await host.VerifyAsync(Alice, third, NextClient())).Content.ReadAsStringAsync());
        Assert.Equal(ResetFailed, await (await host.ResetAsync(Alice, third, NewPassword, NextClient())).Content.ReadAsStringAsync());
        Assert.Equal(HttpStatusCode.OK, (await host.LoginAsync(Alice, OldPassword)).StatusCode);

        host.Time.Advance(TimeSpan.FromDays(1));
        await host.ForgetPasswordAsync(Alice, NextClient());
        Assert.Equal(HttpStatusCode.OK, (await host.ResetAsync(Alice, host.Sent.LatestCodeFor(Alice), NewPassword, NextClient())).StatusCode);
    }

    [Fact]
    public async Task Checks_without_a_live_code_do_not_use_up_the_account_budget()
    {
        await using var host = await PasswordResetTestHost.StartAsync();
        await host.AddUserAsync(Alice, OldPassword);

        // No code issued yet.
        for (var check = 0; check < 10; check++)
        {
            await host.VerifyAsync(Alice, "123456", NextClient());
            await host.ResetAsync(Alice, "123456", NewPassword, NextClient());
        }

        // A code that has expired.
        await host.ForgetPasswordAsync(Alice, NextClient());
        var expired = host.Sent.LatestCodeFor(Alice);
        host.Time.Advance(TimeSpan.FromMinutes(16));
        for (var check = 0; check < 5; check++)
            await host.VerifyAsync(Alice, expired, NextClient());

        await host.ForgetPasswordAsync(Alice, NextClient());
        var live = host.Sent.LatestCodeFor(Alice);

        Assert.Equal(HttpStatusCode.OK, (await host.VerifyAsync(Alice, live, NextClient())).StatusCode);
        Assert.Equal(HttpStatusCode.OK, (await host.ResetAsync(Alice, live, NewPassword, NextClient())).StatusCode);
        Assert.Equal(HttpStatusCode.OK, (await host.LoginAsync(Alice, NewPassword)).StatusCode);
    }

    [Fact]
    public void Concurrent_checks_can_never_exceed_the_account_budget()
    {
        var throttle = new InMemoryPasswordResetThrottle(new ResetTestClock());

        var reserved = 0;
        Parallel.For(0, 64, _ =>
        {
            if (throttle.TryReserveCheck(Alice))
                Interlocked.Increment(ref reserved);
        });

        Assert.Equal(InMemoryPasswordResetThrottle.FailedChecksPerDay, reserved);
    }

    [Fact]
    public void A_matching_check_gives_its_reservation_back()
    {
        var throttle = new InMemoryPasswordResetThrottle(new ResetTestClock());

        for (var check = 0; check < 50; check++)
        {
            Assert.True(throttle.TryReserveCheck(Alice));
            throttle.ReleaseCheck(Alice);
        }

        Assert.True(throttle.TryReserveCheck(Alice.ToUpperInvariant()));
    }

    [Fact]
    public async Task ForgetPassword_answers_before_the_email_is_sent()
    {
        var sender = new BlockingEmailSender();
        await using var host = await PasswordResetTestHost.StartAsync(sender);
        await host.AddUserAsync(Alice, OldPassword);
        try
        {
            var response = await host.Client
                .SendAsync(PasswordResetTestHost.Post("api/Authentication/ForgetPassword", new { email = Alice }))
                .WaitAsync(TimeSpan.FromSeconds(5));

            Assert.Equal(HttpStatusCode.OK, response.StatusCode);
            Assert.Contains(AuthenticationController.ForgetPasswordMessage, await response.Content.ReadAsStringAsync());
            Assert.False(sender.Completed);
        }
        finally
        {
            sender.Release();
        }

        await host.WaitForEmailDrainAsync();
        Assert.True(sender.Completed);
    }

    [Fact]
    public async Task An_unregistered_email_gets_the_same_database_write_but_a_code_nothing_can_match()
    {
        await using var host = await PasswordResetTestHost.StartAsync();
        var alice = await host.AddUserAsync(Alice, OldPassword);

        await host.ForgetPasswordAsync(Alice);
        await host.ForgetPasswordAsync("nobody@example.com");

        var rows = await host.PendingCodesAsync();
        Assert.Equal(2, rows.Count);
        var registered = Assert.Single(rows, row => row.Email == Alice);
        var unregistered = Assert.Single(rows, row => row.Email == "nobody@example.com");
        Assert.Equal(alice.Id, registered.UserId);
        Assert.Equal(string.Empty, unregistered.UserId);
        Assert.Matches("^[0-9a-f]{64}$", unregistered.CodeHash);
        Assert.Equal(registered.ExpiresAtUtc, unregistered.ExpiresAtUtc);
        Assert.Single(host.Sent.Messages);

        Assert.Equal(CodeNotMatched, await (await host.VerifyAsync("nobody@example.com", "000000")).Content.ReadAsStringAsync());
    }

    [Fact]
    public async Task Each_request_clears_expired_codes_so_decoy_rows_do_not_accumulate()
    {
        await using var host = await PasswordResetTestHost.StartAsync();

        await host.ForgetPasswordAsync("first@example.com");
        await host.ForgetPasswordAsync("second@example.com");
        host.Time.Advance(TimeSpan.FromMinutes(16));
        await host.ForgetPasswordAsync("third@example.com");

        var row = Assert.Single(await host.PendingCodesAsync());
        Assert.Equal("third@example.com", row.Email);
    }

    [Fact]
    public async Task A_code_stored_in_the_previous_unkeyed_format_no_longer_matches()
    {
        await using var host = await PasswordResetTestHost.StartAsync();
        var alice = await host.AddUserAsync(Alice, OldPassword);
        var code = await host.AddSiblingCodeAsync(Alice, alice.Id, keyedHash: false);

        Assert.Equal(CodeNotMatched, await (await host.VerifyAsync(Alice, code)).Content.ReadAsStringAsync());
        Assert.Equal(ResetFailed, await (await host.ResetAsync(Alice, code, NewPassword)).Content.ReadAsStringAsync());
    }

    [Fact]
    public void A_code_hashed_under_another_server_secret_does_not_match()
    {
        var salt = PasswordResetCodeSecrets.NewSalt();
        var hash = PasswordResetCodeSecrets.Hash(PasswordResetCodeSecrets.DeriveKey(new string('a', 64)), salt, "123456");

        Assert.True(PasswordResetCodeSecrets.Matches(PasswordResetCodeSecrets.DeriveKey(new string('a', 64)), salt, "123456", hash));
        Assert.False(PasswordResetCodeSecrets.Matches(PasswordResetCodeSecrets.DeriveKey(new string('b', 64)), salt, "123456", hash));
    }

    [Fact]
    public async Task Reset_queue_and_throttle_are_process_wide_and_the_sender_runs()
    {
        await using var host = await PasswordResetTestHost.StartAsync();

        object Resolve<T>() where T : notnull
        {
            using var scope = host.Services.CreateScope();
            return scope.ServiceProvider.GetRequiredService<T>();
        }

        Assert.Same(Resolve<IPasswordResetEmailQueue>(), Resolve<IPasswordResetEmailQueue>());
        Assert.Same(Resolve<IPasswordResetThrottle>(), Resolve<IPasswordResetThrottle>());
        Assert.Same(Resolve<PasswordResetEmailChannel>(), Resolve<IPasswordResetEmailQueue>());
        Assert.Contains(host.Services.GetServices<IHostedService>(), service => service is PasswordResetEmailSenderHostedService);
    }

    private static string WrongCode(string code) =>
        ((int.Parse(code) + 1) % 1_000_000).ToString("D6");

    private sealed class BlockingEmailSender : IEmailSender
    {
        private readonly TaskCompletionSource _gate = new(TaskCreationOptions.RunContinuationsAsynchronously);

        public bool Completed { get; private set; }

        public void Release() => _gate.TrySetResult();

        public async Task<bool> SendEmailAsync(string emailTo, string subject, string body)
        {
            await _gate.Task;
            Completed = true;
            return true;
        }
    }
}