HOWTO: Retrieve a DCOM clients Authentication Level

ID: Q186274

The information in this article applies to:

SUMMARY

There are specific network situations where you will need to specify DCOM security settings on a remote client machine. You do not want to ask your end-users to open and use DCOMCNFG.EXE before they can run the DCOM client on their machines. As of version 1.1 of DCOM95, you can now specify process- specific security for a DCOM client running on a Windows 95 or Windows 98 machine. Please see the DCOM release notes for more information regarding this feature. This article contains a function that can be used to retrieve a DCOM client's Authentication Level from within a Visual Basic program.


MORE INFORMATION

The GetAuthentication function:

By providing this function with your DCOM clients exe name you can retrieve the current authentication level (1-None, 2-Connect).

NOTE: This does not work with Windows NT 4.0 Service Packs 3 or earlier. This functionality will be available in later versions of Windows NT.

This article reads a registry key that will not be available by default. Refer to the complimentary article Q186275: HOWTO: Set DCOM Client's Authentication Level Programmatically.

Step-by-Step Procedure

  1. Open the Visual Basic project to which you want to add this function.


  2. Add the following code to a standard module in your project:
    
      Option Explicit
      'registry api constants and functions
      Private Const REG_SZ = 1
      Private Const REG_DWORD = 4
      Private Const HKEY_CLASSES_ROOT = &H80000000
      Private Const ERROR_SUCCESS = 0
      Private Const ERROR_NONE = 0
      Private Const KEY_ALL_ACCESS = &H3F

      Private Declare Function RegCloseKey Lib "advapi32.dll" _
       (ByVal hKey As Long) As Long
      Private Declare Function RegOpenKey Lib "advapi32.dll" _
       Alias "RegOpenKeyA" _
       (ByVal hKey As Long, ByVal lpSubKey As String, _
       phkResult As Long) As Long
      Private Declare Function RegOpenKeyEx Lib "advapi32.dll" _
       Alias "RegOpenKeyExA" _
       (ByVal hKey As Long, ByVal lpSubKey As String, _
       ByVal ulOptions As Long, ByVal samDesired As Long, _
       phkResult As Long) As Long
      Private Declare Function RegQueryValue Lib "advapi32.dll" _
       Alias "RegQueryValueA" _
       (ByVal hKey As Long, ByVal lpSubKey As String, _
       ByVal lpValue As String, lpcbValue As Long) As Long
      Private Declare Function RegQueryValueEx Lib "advapi32.dll" _
       Alias "RegQueryValueExA" _
       (ByVal hKey As Long, ByVal lpValueName As String, _
       ByVal lpReserved As Long, lpType As Long, lpData As Any, _
       lpcbData As Long) As Long
      Private Declare Function RegSetValueEx Lib "advapi32.dll" _
       Alias "RegSetValueExA" _
       (ByVal hKey As Long, ByVal lpValueName As String, _
       ByVal Reserved As Long, ByVal dwType As Long, lpData As Any, _
       ByVal cbData As Long) As Long

      Public Function GetAuthentication(ClassName As String) As Integer
       Dim lRetVal As Long      'result of the API functions
       Dim hKey As Long         'handle of opened key
       Dim sKeyName As String
       Dim lpType As Long
       Dim lpData As String
       Dim lpData2 As Long
       Dim lpcbData As Long
       Dim myappid As String
       Dim auth As Integer

        If ClassName = "" Then
         GetAuthentication = -1
         MsgBox "Invalid class name"
         Exit Function
        End If
        sKeyName = ClassName
        lRetVal = RegOpenKey(HKEY_CLASSES_ROOT, sKeyName, hKey)
        If lRetVal = ERROR_SUCCESS Then
         lpcbData = 40
         lpData = Space$(40)
         lRetVal = RegQueryValue(hKey, "CLSID", lpData, lpcbData)

         If lRetVal = ERROR_NONE Then
          myappid = Left$(lpData, lpcbData - 1)
          RegCloseKey (hKey)
          sKeyName = "AppID\" & myappid
          lRetVal = RegOpenKeyEx(HKEY_CLASSES_ROOT, sKeyName, 0&, _
          KEY_ALL_ACCESS, hKey)
          If lRetVal = ERROR_SUCCESS Then
           lpData2 = CLng(0)
           lpcbData = Len(lpData2)
           lpType = REG_DWORD
           lRetVal = RegQueryValueEx(hKey, "AuthenticationLevel", 0&, _
           lpType, lpData2, lpcbData)
           If lRetVal = ERROR_NONE Then
            auth = CInt(lpData2)
            GetAuthentication = auth
           Else
            MsgBox lRetVal & " - Unable to read authentication level."
            GetAuthentication = -2
           End If
          Else
           MsgBox lRetVal & " - Cannot find AppID for " & sKeyName
           GetAuthentication = -3
          End If
          RegCloseKey (hKey)
         Else
          MsgBox lRetVal & " - Cannot read AppID value for " & sKeyName
          GetAuthentication = -4
         End If
        Else
         MsgBox lRetVal & " - Cannot find exe name - " & sKeyName
         GetAuthentication = -5
        End If
        Exit Function
      QueryValueExExit:
        MsgBox lRetVal & " - Unexpected error"
        GetAuthentication = -7
        Exit Function
      QueryValueExError:
        Resume QueryValueExExit
      End Function


  3. You can now call this function from anywhere within the project.


  4. Add the call to GetAuthentication to your project using the following syntax:
    
      Dim iSetAuth As Integer
      iSetAuth = GetAuthentication("YourDCOMServer.YourFirstClass")
      If iSetAuth < 1 Then
         MsgBox "Error retrieving authentication level: " & iSetAuth
      End If


  5. Change the parameter to the name of your remote server's first class.


  6. The function will return an integer less than zero if an error occurred, a 1 for No authentication, or a 2 for Connect authentication.



REFERENCES

There is a complimentary article that is the reverse of this function and named SetAuthentication. This function will set the current authentication level for a registered remote server on the client machine. For more information regarding the SetAuthentication function please see the following article in the Microsoft Knowledge Base:

Q186275 : HOWTO: Set DCOM Client's Authentication Level Programmatically

For more information regarding DCOM security and the usage of DCOMCNFG.EXE, please see the following article in the Microsoft Knowledge Base:
Q183607 : HOWTO: Configure DCOM for Visual Basic 5.0 Using DCOMCNFG.EXE

For more information regarding advanced DCOM functionality that might require these client side security settings, please see the following article in the Microsoft Knowledge Base:
Q175510 : FILE: VB5 DCOM Demonstration using Callbacks and WithEvents

(c) Microsoft Corporation 1998, All Rights Reserved. Contributions by Randy Russell, Microsoft Corporation

Additional query words: DCOMCNFG.EXE permissions security error 70 error 429 kbDSupport kbdse
kbVBp500 kbWinOS98 kbVBp 


Keywords          : 
Version           : WINDOWS:5.0
Platform          : WINDOWS 
Issue type        : kbhowto

Last Reviewed: May 19, 1999