/* Copyright (c) 1996-2016, OPC Foundation. All rights reserved.
   The source code in this file is covered under a dual-license scenario:
     - RCL: for OPC Foundation members in good-standing
     - GPL V2: everybody else
   RCL license terms accompanied with this source code. See http://opcfoundation.org/License/RCL/1.00/
   GNU General Public License as published by the Free Software Foundation;
   version 2 of the License are accompanied with this source code. See http://opcfoundation.org/License/GPLv2
   This source code is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
*/

using Opc.Ua.Server;
using System;
using System.Collections.Generic;
using System.Security.Cryptography.X509Certificates;
using System.Text;
using System.Xml;

namespace Opc.Ua.Sample
{
    public partial class SampleServer
    {
        #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];

                // ignore policies without an explicit id.
                if (String.IsNullOrEmpty(policy.PolicyId))
                {
                    continue;
                }
                
                // create a validator for an issued token policy.
                if (policy.TokenType == UserTokenType.IssuedToken)
                {
                    // the name of the element in the configuration file.
                    XmlQualifiedName qname = new XmlQualifiedName(policy.PolicyId, Namespaces.OpcUa);

                    // find the id for the issuer certificate.
                    CertificateIdentifier id = configuration.ParseExtension<CertificateIdentifier>(qname);
                    
                    if (id == null)
                    {
                        Utils.Trace(
                            (int)Utils.TraceMasks.Error, 
                            "Could not load CertificateIdentifier for UserTokenPolicy {0}", 
                            policy.PolicyId);

                        continue;
                    }
               }
                
                // create a validator for a certificate token policy.
                if (policy.TokenType == UserTokenType.Certificate)
                {
                    // the name of the element in the configuration file.
                    XmlQualifiedName qname = new XmlQualifiedName(policy.PolicyId, Namespaces.OpcUa);
                    
                    // find the location of the trusted issuers.
                    CertificateTrustList trustedIssuers = configuration.ParseExtension<CertificateTrustList>(qname);
                    
                    if (trustedIssuers == null)
                    {
                        Utils.Trace(
                            (int)Utils.TraceMasks.Error, 
                            "Could not load CertificateTrustList for UserTokenPolicy {0}", 
                            policy.PolicyId);

                        continue;
                    }

                    // trusts any certificate in the trusted people store.
                    m_certificateValidator = new X509CertificateValidator();
                }
            }
        }

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

            // check for a user name token.
            UserNameIdentityToken userNameToken = args.NewIdentity as UserNameIdentityToken;
            
            if (userNameToken != null)
            {
                VerifyPassword(userNameToken.UserName, userNameToken.DecryptedPassword);
                args.Identity = new UserIdentity(userNameToken);
                Utils.Trace("UserName Token Accepted: {0}", args.Identity.DisplayName);
                return;
            }

            // check for x509 user token.
            X509IdentityToken x509Token = args.NewIdentity as X509IdentityToken;
            
            if (userNameToken != null)
            {
                VerifyCertificate(x509Token.Certificate);
                args.Identity = new UserIdentity(x509Token);
                Utils.Trace("X509 Token Accepted: {0}", args.Identity.DisplayName);
                return;
            }
        }

        /// <summary>
        /// Validates the password for a username token.
        /// </summary>
        private void VerifyPassword(string userName, string password)
        {                   
            if (String.IsNullOrEmpty(password))
            {
                // construct translation object with default text.
                TranslationInfo info = new TranslationInfo(
                    "InvalidPassword",
                    "en-US",
                    "Specified password is not valid for user '{0}'.",
                    userName);

                // create an exception with a vendor defined sub-code.
                throw new ServiceResultException(new ServiceResult(
                    StatusCodes.BadIdentityTokenRejected,
                    "InvalidPassword",
                    "http://opcfoundation.org/UA/Sample/",
                    new LocalizedText(info)));
            }
        }        

        /// <summary>
        /// Verifies that a certificate user token is trusted.
        /// </summary>
        private void VerifyCertificate(X509Certificate2 certificate)
        {        
            try
            {
                m_certificateValidator.Validate(certificate);
            }
            catch (Exception e)
            {
                // construct translation object with default text.
                TranslationInfo info = new TranslationInfo(
                    "InvalidCertificate",
                    "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(
                    e,
                    StatusCodes.BadIdentityTokenRejected,
                    "InvalidCertificate",
                    "http://opcfoundation.org/UA/Sample/",
                    new LocalizedText(info)));
            }
        }     
        #endregion
        
        #region Private Fields
        private X509CertificateValidator m_certificateValidator; 
        #endregion 
    }
}