source: TFP-WebServer/WebServer/src/Permissions/AdminWebUsers.cs@ 499

using System;
using System.Collections.Generic;
using System.Text;
using System.Xml;

namespace Webserver.Permissions {
        public class AdminWebUsers : AdminSectionAbs {
                public static AdminWebUsers Instance { get; private set; }

                public AdminWebUsers (AdminTools _parent) : base (_parent, "webusers") {
                        Instance = this;
                }

                private readonly Dictionary<string, WebUser> users = new CaseInsensitiveStringDictionary<WebUser> ();


#region IO

                public override void Clear () {
                        users.Clear ();
                }

                public override void ParseElement (XmlElement _childElement) {
                        if (WebUser.TryParse (_childElement, out WebUser webUser)) {
                                users [webUser.Name] = webUser;
                        }
                }

                public override void Save (XmlElement _root) {
                        XmlElement usersElement = _root.AddXmlElement (SectionTypeName);
                        // modulesElement.AddXmlComment (" <module name=\"adminuser1\" secret=\"supersecrettoken\" permission_level=\"0\" /> ");

                        foreach ((string _, WebUser module) in users) {
                                module.ToXml (usersElement);
                        }
                }

#endregion


#region Runtime interaction


                public void AddUser (string _name, string _password, PlatformUserIdentifierAbs _userIdentifier, PlatformUserIdentifierAbs _crossPlatformIdentifier) {
                        lock (Parent) {
                                WebUser p = new WebUser (_name, _password, _userIdentifier, _crossPlatformIdentifier);

                                // TODO: Check if another name exists with the same (crossplatform)identifier, remove that
                                users[_name] = p;

                                Parent.Save ();
                        }
                }

                public bool RemoveUser (string _name) {
                        lock (Parent) {
                                bool removed = users.Remove (_name);
                                if (removed) {
                                        Parent.Save ();
                                }

                                return removed;
                        }
                }

                public Dictionary<string, WebUser> GetUsers () {
                        lock (Parent) {
                                return users;
                        }
                }

#endregion

                public readonly struct WebUser {
                        public readonly string Name;
                        public readonly byte[] PasswordHash;
                        public readonly PlatformUserIdentifierAbs PlatformUser;
                        public readonly PlatformUserIdentifierAbs CrossPlatformUser;

                        public WebUser (string _name, byte[] _passwordHash, PlatformUserIdentifierAbs _platformUser, PlatformUserIdentifierAbs _crossPlatformUser) {
                                Name = _name;
                                PasswordHash = _passwordHash;
                                PlatformUser = _platformUser;
                                CrossPlatformUser = _crossPlatformUser;
                        }
                        
                        public WebUser (string _name, string _password, PlatformUserIdentifierAbs _platformUser, PlatformUserIdentifierAbs _crossPlatformUser) {
                                Name = _name;
                                PasswordHash = Hash (_password);
                                PlatformUser = _platformUser;
                                CrossPlatformUser = _crossPlatformUser;
                        }

                        public void ToXml (XmlElement _parent) {
                                XmlElement elem = _parent.AddXmlElement ("user");
                                elem.SetAttrib ("name", Name)
                                        .SetAttrib ("pass", Convert.ToBase64String(PasswordHash));
                                PlatformUser.ToXml (elem);
                                CrossPlatformUser?.ToXml (elem, "cross");
                        }

                        public static bool TryParse (XmlElement _element, out WebUser _result) {
                                _result = default;

                                if (!_element.TryGetAttribute ("name", out string name)) {
                                        Log.Warning ($"[Web] [Perms] Ignoring user-entry because of missing 'name' attribute: {_element.OuterXml}");
                                        return false;
                                }

                                if (!_element.TryGetAttribute ("pass", out string passHashString)) {
                                        Log.Warning ($"[Web] [Perms] Ignoring user-entry because of missing 'pass' attribute: {_element.OuterXml}");
                                        return false;
                                }

                                PlatformUserIdentifierAbs userIdentifier = PlatformUserIdentifierAbs.FromXml (_element, false);
                                if (userIdentifier == null) {
                                        Log.Warning ($"[Web] [Perms] Ignoring user-entry because of missing 'platform' or 'userid' attribute: {_element.OuterXml}");
                                        return false;
                                }

                                PlatformUserIdentifierAbs crossIdentifier = PlatformUserIdentifierAbs.FromXml (_element, false, "cross");

                                byte[] passHash = Convert.FromBase64String (passHashString);

                                _result = new WebUser (name, passHash, userIdentifier, crossIdentifier);
                                return true;
                        }

                        public bool ValidatePassword (string _password) {
                                byte[] input = Hash (_password);
                                return Utils.ArrayEquals (input, PasswordHash);
                        }
                }

                private static byte[] Hash (string _input) {
                        System.Security.Cryptography.MD5Cng hasherMD5 = new System.Security.Cryptography.MD5Cng();

                        return hasherMD5.ComputeHash (Encoding.UTF8.GetBytes (_input));
                }

                public bool TryGetUser (string _name, string _password, out WebUser _result) {
                        lock (Parent) {
                                if (users.TryGetValue (_name, out _result) && _result.ValidatePassword (_password)) {
                                        return true;
                                }

                                _result = default;
                                return false;
                        }
                }

                public bool HasUser (PlatformUserIdentifierAbs _platformUser, PlatformUserIdentifierAbs _crossPlatformUser, out WebUser _result) {
                        lock (Parent) {
                                _result = default;

                                foreach ((string _, WebUser webUser) in users) {
                                        if (!Equals (webUser.PlatformUser, _platformUser) ||
                                            !Equals (webUser.CrossPlatformUser, _crossPlatformUser)) {
                                                continue;
                                        }

                                        _result = webUser;
                                        return true;
                                }

                                return false;
                        }
                }

        }
}