Can this user log in through the Client? If this application is running as a service, keep in mind it will use the service login, not the current Windows user.

yes this user can log in to client. I am not using service. I am trying it into web application.

See Brian's post above.

I tried with Logon user function and it is working but it requires password also. How do I have user's password. How it is working with SharePoint Windows Authentication mode? Provide me some good post which has correct information for Windows Authentication.

There are a few things you need to take into consideration when trying to do SSO through IIS. First and foremost, the browser will not pass the credentials to the server if the url is not considered to be on the intranet. For example, if you have a web address of "https://webserver.domain.local/login.aspx" then the browser will not send the credentials to the server. This article outlines it pretty well. It says only Internet Explorer, but it is the same for all browsers. There are a few more things to consider, but this one ate my lunch.

I am focusing on this code:

RA [C#]

// Using the Server object to retrieve list of repositories
Server myServ = new Server("MyServerName");
RepositoryRegistrationCollection repoRegColl = myServ.GetRepositories();
RepositoryRegistration myRepoReg = repoRegColl["MyRepositoryName"];
Session mySess = new Session();
mySess.LogIn(myRepoReg); // Use current thread's Windows credentials.

Here it is mentioned that without username and password it will check for windows credentials then why it is not working. Browser related changes I need to do for all users. If you open SharePoint Site with Laserfiche webparts then we do not require to set anything.

I am trying the above code in SharePoint but it is not working where my site is already enabled for Windows Authentication.

I need a working code to Login using Windows Authentication.

Normally you do not want to use the current thread's Windows credentials, since the host process is running as a low-trust local account.  Have you read the thread I linked to in my initial response?  Your code does no impersonating.  Is Kerberos correctly configured?

And if you are running under SharePoint, it may be more complicated.  You may find that the Identity you get from the user's context is not a WindowsIdentity, but is a ClaimsIdentity instead.  I believe there is a setting on your SharePoint site that controls which one you get.  The WindowsIdentity is easier to work with, otherwise you need to convert the ClaimsIdentity to a WindowsIdentity, by calling into the C2WTS service via the S4U library.  This identity only works with Kerberos constrained delegation, and you also need to grant access to the C2WTS service.  You should check out the documentation for the Web Access SharePoint integration.

Let me find out the document and check it. You can send me link for the updated document, if you have.

I also tried the code:

try
{
   var current = System.Security.Principal.WindowsIdentity.GetCurrent();
   WindowsIdentity clientID = (WindowsIdentity)HttpContext.Current.User.Identity;
   using (wic = clientID.Impersonate()) {
      // Log into Repository
      RepositoryRegistration MyRepository = new RepositoryRegistration(servername, reponame);
      Session newsession = new Session();               
      newsession.LogIn(MyRepository);
      MySession = newsession;
   }
}

catch (Exception e)
{
   error = e.Message;
}

but it is also not getting validated.

Have you trusted the machine for delegation so that Kerberos will work properly?  That is a requirement.

how to do that?