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 * OPC Foundation MIT License 1.00
 * 
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 * obtaining a copy of this software and associated documentation
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using System;
using System.Collections.Generic;
using System.Linq;
using System.Reflection;
using System.Security.Cryptography.X509Certificates;
using Opc.Ua;
using Opc.Ua.Server;

namespace Quickstarts.ReferenceServer
{
    /// <summary>
    /// Implements the Quickstart Reference Server.
    /// </summary>
    /// <remarks>
    /// Each server instance must have one instance of a StandardServer object which is
    /// responsible for reading the configuration file, creating the endpoints and dispatching
    /// incoming requests to the appropriate handler.
    /// 
    /// This sub-class specifies non-configurable metadata such as Product Name and initializes
    /// the EmptyNodeManager which provides access to the data exposed by the Server.
    /// </remarks>
    public partial class ReferenceServer : ReverseConnectServer
    {
        #region Overridden Methods
        /// <summary>
        /// Creates the node managers for the server.
        /// </summary>
        /// <remarks>
        /// This method allows the sub-class create any additional node managers which it uses. The SDK
        /// always creates a CoreNodeManager which handles the built-in nodes defined by the specification.
        /// Any additional NodeManagers are expected to handle application specific nodes.
        /// </remarks>
        protected override MasterNodeManager CreateMasterNodeManager(IServerInternal server, ApplicationConfiguration configuration)
        {


            // create the custom node managers.
            nodeManagers.Add(new ReferenceNodeManager(server, configuration));

            if (m_nodeManagerFactory == null || m_nodeManagerFactory.Count == 0)
            {
                AddDefaultFactories();
            }

            foreach (var nodeManagerFactory in m_nodeManagerFactory)
            {
                nodeManagers.Add(nodeManagerFactory.Create(server, configuration));
            }

            // create master node manager.
            return new MasterNodeManager(server, configuration, null, nodeManagers.ToArray());
        }

        /// <summary>
        /// Loads the non-configurable properties for the application.
        /// </summary>
        /// <remarks>
        /// These properties are exposed by the server but cannot be changed by administrators.
        /// </remarks>
        protected override ServerProperties LoadServerProperties()
        {
            ServerProperties properties = new ServerProperties();

            properties.ManufacturerName = "OPC Foundation";
            properties.ProductName = "Quickstart Reference Server";
            properties.ProductUri = "http://opcfoundation.org/Quickstart/ReferenceServer/v1.04";
            properties.SoftwareVersion = Utils.GetAssemblySoftwareVersion();
            properties.BuildNumber = Utils.GetAssemblyBuildNumber();
            properties.BuildDate = Utils.GetAssemblyTimestamp();

            return properties;
        }

        /// <summary>
        /// Creates the resource manager for the server.
        /// </summary>
        protected override ResourceManager CreateResourceManager(IServerInternal server, ApplicationConfiguration configuration)
        {
            ResourceManager resourceManager = new ResourceManager(server, configuration);

            System.Reflection.FieldInfo[] fields = typeof(StatusCodes).GetFields(System.Reflection.BindingFlags.Public | System.Reflection.BindingFlags.Static);

            foreach (System.Reflection.FieldInfo field in fields)
            {
                uint? id = field.GetValue(typeof(StatusCodes)) as uint?;

                if (id != null)
                {
                    resourceManager.Add(id.Value, "en-US", field.Name);
                }
            }

            return resourceManager;
        }

        /// <summary>
        /// Initializes the server before it starts up.
        /// </summary>
        /// <remarks>
        /// This method is called before any startup processing occurs. The sub-class may update the 
        /// configuration object or do any other application specific startup tasks.
        /// </remarks>
        protected override void OnServerStarting(ApplicationConfiguration configuration)
        {

            base.OnServerStarting(configuration);

            // it is up to the application to decide how to validate user identity tokens.
            // this function creates validator for X509 identity tokens.
            CreateUserIdentityValidators(configuration);
        }

        /// <summary>
        /// Called after the server has been started.
        /// </summary>
        protected override void OnServerStarted(IServerInternal server)
        {
            base.OnServerStarted(server);

            // request notifications when the user identity is changed. all valid users are accepted by default.
            server.SessionManager.ImpersonateUser += new ImpersonateEventHandler(SessionManager_ImpersonateUser);

            try
            {
                lock (ServerInternal.Status.Lock)
                {
                    // allow a faster sampling interval for CurrentTime node.
                    ServerInternal.Status.Variable.CurrentTime.MinimumSamplingInterval = 250;
                }
            }
            catch
            { }

        }
        #endregion

        #region User Validation Functions
        /// <summary>
        /// Creates the objects used to validate the user identity tokens supported by the server.
        /// </summary>
        private void CreateUserIdentityValidators(ApplicationConfiguration configuration)
        {
            for (int ii = 0; ii < configuration.ServerConfiguration.UserTokenPolicies.Count; ii++)
            {
                UserTokenPolicy policy = configuration.ServerConfiguration.UserTokenPolicies[ii];

                // create a validator for a certificate token policy.
                if (policy.TokenType == UserTokenType.Certificate)
                {
                    // check if user certificate trust lists are specified in configuration.
                    if (configuration.SecurityConfiguration.TrustedUserCertificates != null &&
                        configuration.SecurityConfiguration.UserIssuerCertificates != null)
                    {
                        CertificateValidator certificateValidator = new CertificateValidator();
                        certificateValidator.Update(configuration.SecurityConfiguration).Wait();
                        certificateValidator.Update(configuration.SecurityConfiguration.UserIssuerCertificates,
                            configuration.SecurityConfiguration.TrustedUserCertificates,
                            configuration.SecurityConfiguration.RejectedCertificateStore);

                        // set custom validator for user certificates.
                        m_userCertificateValidator = certificateValidator.GetChannelValidator();
                    }
                }
            }
        }

        /// <summary>
        /// Called when a client tries to change its user identity.
        /// </summary>
        private void SessionManager_ImpersonateUser(Session session, ImpersonateEventArgs args)
        {
            // check for a user name token.
            UserNameIdentityToken userNameToken = args.NewIdentity as UserNameIdentityToken;

            if (userNameToken != null)
            {
                args.Identity = VerifyPassword(userNameToken);
                
                // set AuthenticatedUser role for accepted user/password authentication
                args.Identity.GrantedRoleIds.Add(ObjectIds.WellKnownRole_AuthenticatedUser);

                if (args.Identity is SystemConfigurationIdentity)
                {
                    // set ConfigureAdmin role for user with permission to configure server
                    args.Identity.GrantedRoleIds.Add(ObjectIds.WellKnownRole_ConfigureAdmin);
                    args.Identity.GrantedRoleIds.Add(ObjectIds.WellKnownRole_SecurityAdmin);
                }

                return;
            }

            // check for x509 user token.
            X509IdentityToken x509Token = args.NewIdentity as X509IdentityToken;

            if (x509Token != null)
            {
                VerifyUserTokenCertificate(x509Token.Certificate);
                args.Identity = new UserIdentity(x509Token);
                
                // set AuthenticatedUser role for accepted certificate authentication
                args.Identity.GrantedRoleIds.Add(ObjectIds.WellKnownRole_AuthenticatedUser);

                return;
            }

            // check for anonymous token.
            if (args.NewIdentity is AnonymousIdentityToken || args.NewIdentity == null)
            {
                // allow anonymous authentication and set Anonymous role for this authentication
                args.Identity = new UserIdentity();
                args.Identity.GrantedRoleIds.Add(ObjectIds.WellKnownRole_Anonymous);

                return;
            }

            // unsuported identity token type.
            throw ServiceResultException.Create(StatusCodes.BadIdentityTokenInvalid,
                   "Not supported user token type: {0}.", args.NewIdentity);
        }

        /// <summary>
        /// Validates the password for a username token.
        /// </summary>
        private IUserIdentity VerifyPassword(UserNameIdentityToken userNameToken)
        {
            var userName = userNameToken.UserName;
            var password = userNameToken.DecryptedPassword;
            if (String.IsNullOrEmpty(userName))
            {
                // an empty username is not accepted.
                throw ServiceResultException.Create(StatusCodes.BadIdentityTokenInvalid,
                    "Security token is not a valid username token. An empty username is not accepted.");
            }

            if (String.IsNullOrEmpty(password))
            {
                // an empty password is not accepted.
                throw ServiceResultException.Create(StatusCodes.BadIdentityTokenRejected,
                    "Security token is not a valid username token. An empty password is not accepted.");
            }

            // User with permission to configure server
            if (userName == "sysadmin" && password == "demo")
            {
                return new SystemConfigurationIdentity(new UserIdentity(userNameToken));
            }

            // standard users for CTT verification
            if (!((userName == "user1" && password == "password") ||
                (userName == "user2" && password == "password1")))
            {
                // construct translation object with default text.
                TranslationInfo info = new TranslationInfo(
                    "InvalidPassword",
                    "en-US",
                    "Invalid username or password.",
                    userName);

                // create an exception with a vendor defined sub-code.
                throw new ServiceResultException(new ServiceResult(
                    StatusCodes.BadUserAccessDenied,
                    "InvalidPassword",
                    LoadServerProperties().ProductUri,
                    new LocalizedText(info)));
            }

            return new UserIdentity(userNameToken);
        }

        /// <summary>
        /// Verifies that a certificate user token is trusted.
        /// </summary>
        private void VerifyUserTokenCertificate(X509Certificate2 certificate)
        {
            try
            {
                if (m_userCertificateValidator != null)
                {
                    m_userCertificateValidator.Validate(certificate);
                }
                else
                {
                    CertificateValidator.Validate(certificate);
                }
            }
            catch (Exception e)
            {
                TranslationInfo info;
                StatusCode result = StatusCodes.BadIdentityTokenRejected;
                ServiceResultException se = e as ServiceResultException;
                if (se != null && se.StatusCode == StatusCodes.BadCertificateUseNotAllowed)
                {
                    info = new TranslationInfo(
                        "InvalidCertificate",
                        "en-US",
                        "'{0}' is an invalid user certificate.",
                        certificate.Subject);

                    result = StatusCodes.BadIdentityTokenInvalid;
                }
                else
                {
                    // construct translation object with default text.
                    info = new TranslationInfo(
                        "UntrustedCertificate",
                        "en-US",
                        "'{0}' is not a trusted user certificate.",
                        certificate.Subject);
                }

                // create an exception with a vendor defined sub-code.
                throw new ServiceResultException(new ServiceResult(
                    result,
                    info.Key,
                    LoadServerProperties().ProductUri,
                    new LocalizedText(info)));
            }
        }

        private static INodeManagerFactory IsINodeManagerFactoryType(Type type)
        {
            var nodeManagerTypeInfo = type.GetTypeInfo();
            if (nodeManagerTypeInfo.IsAbstract ||
                !typeof(INodeManagerFactory).IsAssignableFrom(type))
            {
                return null;
            }

            return Activator.CreateInstance(type) as INodeManagerFactory;
        }

        private void AddDefaultFactories()
        {
            var assembly = GetType().Assembly;
            var factories = assembly.GetExportedTypes().Select(type => IsINodeManagerFactoryType(type)).Where(type => type != null);
            m_nodeManagerFactory = new List<INodeManagerFactory>();
            foreach (var nodeManagerFactory in factories)
            {
                m_nodeManagerFactory.Add(nodeManagerFactory);
            }
        }
        #endregion

        #region Private Fields
        private IList<INodeManagerFactory> m_nodeManagerFactory;
        private ICertificateValidator m_userCertificateValidator;
        #endregion


        public List<INodeManager> nodeManagers = new List<INodeManager>();
    }
}