Security DLL

Hi All,
I am writing several small applications and I am looking to serure them to our network.
I can check that the running compuiter is on the company domain and that it can see the application logfile. If either of these fail it will display a message and close the application. This works fine if the code in in the app but I want to use the same code for several apps.
How do I do this in a DLL, identify the calling application and on error close the calling app?

I'm sure there is a simply way to do this???


Private Sub AccessCheck()

UserName = System.Security.Principal.WindowsIdentity.GetCurre nt.Name
ComputerName = Environment.MachineName
DomainName = Environment.UserDomainName
Accesstime = Date.Now
LogFile = "\\appserver\AppLogs\app.log"
If File.Exists(LogFile) Then

If DomainName = "CompanyDomain" Then
FileOpen(1, LogFile, OpenMode.Append, OpenAccess.Write, OpenShare.LockWrite)
WriteLine(1, Accesstime, UserName, ComputerName, DomainName)

FileClose(1)

Else
Err.Number = 1
Call ErrorCodeHandle()
End If
Else
Err.Number = 2
Call ErrorCodeHandle()
End If


End Sub


Private Sub ErrorCodeHandle()
Select Case Err.Number 'Evaluate the error number.
Case 1 'Incorrect domain
MsgBox("You are not Authorised to use this application...........")
MsgBox("Please contact Support@company.com for assistance, this application wil now close.")
Close()

Case 2 'Unable to locate log file
MsgBox("Unable to locate Application log file, Please ensure you are connected to the correct Domain")
MsgBox("Please contact Support@comapany.com for assistance")
Close()


End Select
End Sub
End Class