Create a NetworkCredential from a SPManagedAccount

        private static NetworkCredential GetManagedAccountCredential(string managedAccount)
        {
            NetworkCredential result = null;
            try
            {
                SPSecurity.RunWithElevatedPrivileges(delegate()
                {
                    SPFarmManagedAccountCollection accounts = new SPFarmManagedAccountCollection(SPFarm.Local);
                    SPManagedAccount account = accounts.FindOrCreateAccount(managedAccount);
                    string[] usernameSplit = account.Username.Split('\\');
                    string username = usernameSplit[1];
                    string domain = usernameSplit[0];
                    var securePassword = (SPEncryptedString)account
                                                            .GetType()
                                                            .GetField("m_Password",
                                                              System.Reflection.BindingFlags.GetField |
                                                              System.Reflection.BindingFlags.Instance |
                                                              System.Reflection.BindingFlags.NonPublic)
                                                            .GetValue(account);
                   // TODO - remove these 3 lines when .Net 4.0 is available and we can create NetworkCredential with SecureString
                    var intptr = System.IntPtr.Zero;
                    var unmanagedString = Marshal.SecureStringToGlobalAllocUnicode(securePassword.SecureStringValue);
                    var password = Marshal.PtrToStringUni(unmanagedString);
                    Marshal.ZeroFreeGlobalAllocUnicode(unmanagedString);
                    result = new NetworkCredential(username, password, domain);
                    password = null;
                });
            }
            catch (Exception ex)
            {
                Logging.LogException("GetManagedAccountCredential", ex);
            }
            return result;
        }