source: TFP-WebServer/WebServer/src/WebAPI/APIs/Permissions/RegisterUser.cs@ 459

using System;
using System.Collections.Generic;
using System.Net;
using System.Text;
using System.Text.RegularExpressions;
using JetBrains.Annotations;
using Utf8Json;
using Webserver.Permissions;
using Webserver.UrlHandlers;

namespace Webserver.WebAPI.APIs.Permissions {
        [UsedImplicitly]
        public class RegisterUser : AbsRestApi {
                private static readonly byte[] jsonPlayerNameKey = JsonWriter.GetEncodedPropertyNameWithBeginObject ("playerName");
                private static readonly byte[] jsonExpirationKey = JsonWriter.GetEncodedPropertyNameWithPrefixValueSeparator ("expirationSeconds");
                
                // TODO: Rate-limiting

                private static readonly Regex userValidationRegex = new Regex ("^\\w{4,16}$", RegexOptions.ECMAScript | RegexOptions.Compiled);
                private static readonly Regex passValidationRegex = new Regex ("^\\w{4,16}$", RegexOptions.ECMAScript | RegexOptions.Compiled);

                public RegisterUser (Web _parentWeb) : base (_parentWeb) {
                }

                protected override void HandleRestGet (RequestContext _context) {
                        string token = _context.RequestPath;

                        if (string.IsNullOrEmpty (token)) {
                                SendEmptyResponse (_context, HttpStatusCode.BadRequest, null, "NO_TOKEN");
                                return;
                        }

                        if (!UserRegistrationTokens.TryValidate (token, out UserRegistrationTokens.RegistrationData regData)) {
                                SendEmptyResponse (_context, HttpStatusCode.NotFound, null, "INVALID_OR_EXPIRED_TOKEN");
                                return;
                        }

                        PrepareEnvelopedResult (out JsonWriter writer);
                        
                        writer.WriteRaw (jsonPlayerNameKey);
                        writer.WriteString (regData.PlayerName);
                        
                        writer.WriteRaw (jsonExpirationKey);
                        writer.WriteDouble ((regData.ExpiryTime - DateTime.Now).TotalSeconds);
                        
                        writer.WriteEndObject ();

                        SendEnvelopedResult (_context, ref writer);
                }

                protected override void HandleRestPost (RequestContext _context, IDictionary<string, object> _jsonInput, byte[] _jsonInputData) {
                        if (!JsonCommons.TryGetJsonField (_jsonInput, "token", out string token)) {
                                SendEmptyResponse (_context, HttpStatusCode.BadRequest, _jsonInputData, "MISSING_TOKEN");
                                return;
                        }

                        if (!JsonCommons.TryGetJsonField (_jsonInput, "username", out string username)) {
                                SendEmptyResponse (_context, HttpStatusCode.BadRequest, _jsonInputData, "MISSING_USERNAME");
                                return;
                        }

                        if (!JsonCommons.TryGetJsonField (_jsonInput, "password", out string password)) {
                                SendEmptyResponse (_context, HttpStatusCode.BadRequest, _jsonInputData, "MISSING_PASSWORD");
                                return;
                        }

                        if (!UserRegistrationTokens.TryValidate (token, out UserRegistrationTokens.RegistrationData regData)) {
                                SendEmptyResponse (_context, HttpStatusCode.Unauthorized, null, "INVALID_OR_EXPIRED_TOKEN");
                                return;
                        }

                        if (!userValidationRegex.IsMatch (username)) {
                                SendEmptyResponse (_context, HttpStatusCode.Unauthorized, _jsonInputData, "INVALID_USERNAME");
                                return;
                        }
                        
                        if (!passValidationRegex.IsMatch (password)) {
                                SendEmptyResponse (_context, HttpStatusCode.Unauthorized, _jsonInputData, "INVALID_PASSWORD");
                                return;
                        }

                        if (AdminWebUsers.Instance.GetUsers ().TryGetValue (username, out AdminWebUsers.WebUser existingMapping)) {
                                // Username already exists

                                if (!PlatformUserIdentifierAbs.Equals (existingMapping.PlatformUser, regData.PlatformUserId) ||
                                    !PlatformUserIdentifierAbs.Equals (existingMapping.CrossPlatformUser, regData.CrossPlatformUserId)) {
                                        // Username already in use by another player
                                        SendEmptyResponse (_context, HttpStatusCode.Unauthorized, _jsonInputData, "DUPLICATE_USERNAME");
                                        return;
                                }
                                
                                // Username used by the same player, allow overwriting his existing login
                        }
                        
                        // Log info
                        string crossplatformidString = regData.CrossPlatformUserId == null ? "" : $", crossplatform ID {regData.CrossPlatformUserId.CombinedString}";
                        Log.Out ($"[Web] User registered: Username '{username}' for platform ID {regData.PlatformUserId.CombinedString}{crossplatformidString}");

                        if (AdminWebUsers.Instance.HasUser (regData.PlatformUserId, regData.CrossPlatformUserId, out AdminWebUsers.WebUser existingUser)) {
                                // Remove existing username of player, only allowing one user per player

                                Log.Out ($"[Web] Re-registration, replacing existing username '{existingUser.Name}'");
                                AdminWebUsers.Instance.RemoveUser (existingUser.Name);
                        }

                        // Add new user
                        AdminWebUsers.Instance.AddUser (username, password, regData.PlatformUserId, regData.CrossPlatformUserId);
                        
                        // Login with new user and return response
                        string remoteEndpointString = _context.Request.RemoteEndPoint!.ToString ();
                        SessionHandler.HandleUserIdLogin (ParentWeb.ConnectionHandler, _context, remoteEndpointString, SessionHandler.userPassLoginName,
                                username, regData.PlatformUserId, regData.CrossPlatformUserId);

                        _context.Response.StatusCode = (int)HttpStatusCode.Created;
                        _context.Response.ContentType = WebUtils.MimePlain;
                        _context.Response.ContentEncoding = Encoding.UTF8;
                        _context.Response.ContentLength64 = 0;
                }

                public override int DefaultPermissionLevel () => AdminWebModules.PermissionLevelGuest;
        }
}