Programmatic Group Manipulation

Managing groups and group membership is typically the core operation for administrators tasked with managing file system security. With Visual Basic, you can use methods of the IADsGroup and IADsUser interfaces to query and manipulate groups in the Windows NT namespace. By employing the code segments in this chapter, you can also access the SAM to create applications that use the default authentication and access control mechanisms for managing Windows NT security. Using this system is more desirable than using JET (MS_Access) databases, the Registry, or other insecure data stores to house application security information.

In addition to basic group-membership manipulation, this chapter will explore a proven best-practice method for managing file system security when you require extremely granular access to the files and directories that make up the structure of an NT File System (NTFS) partition.

You will also continue the creation of the NTAdmin.DLL COM server application you started in Chapter 3, "Container Enumeration Methods and Programmatic Domain Account Policy Manipulation."

Windows NT Security Group Administration

The IADsGroup interface supports full management of group objects in domains or in the individual SAMs used on member servers and NT workstations. Using the IADsGroup interface (see Figure 5.1), you can perform the following functions in a Windows NT namespace:

• Add members to any given group.

• Remove members from any given group.

• Enumerate the members of a group.

• Query whether a given user belongs to a group.

• Query or set the description for any given group.

By adding the Groups method of the IADsUser interface to the above methods, you can also

• Enumerate all groups to which a specific user object has been assigned.

Figure 5.1
Group Memberships dialog box in User Manager for Domains.

Group Binding

To manipulate a group object using ADSI, you must first bind to the desired group object. In general, the following syntax is used to perform the binding:

GetObject("WinNT://" & DomainName & "/" & GroupName & ",group")

Notice that you specified the object class as part of the binding string. This yields better performance than the equivalent classless binding string.

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Tip - Although it is an optional parameter, the class name should always be specified as part of the binding string to avoid ambiguity and to improve binding performance.

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Group Binding Using Visual Basic

To bind a group object using Visual Basic, use the following example as a guide:

Dim Group as IADsGroup
Dim GroupName as String
Dim GroupDomain as String
GroupDomain = "Target_Group_Domain"
GroupName = "Target_Group_Name"Set Group = GetObject("WinNT://" & GroupDomain & "/" & GroupName & ",group")

To perform a binding to a group object in your environment, simply replace the assignments for GroupDomain and GroupName with the appropriate values for your enterprise. With the object bound, you can now manipulate the exposed properties and methods of the IADsGroup interface.

Adding Users to a Group

For most administrators, the addition of user accounts to security groups is bound to enter into his or her daily agenda on a regular basis. To help facilitate these actions in the namespace, the IADsGroup interface exposes the Add method for manipulation of group memberships.

To add a new member to a currently bound group object, use the following general syntax:

Group.Add(ADsPath of User Object)

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Tip - You can explicitly state the ADsPath of the user (WinNT://Domain/User), or you can bind to a user object and then pass in the ADsPath property value to the Add method of the IADsGroup interface.

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Adding Users to a Group Using Visual Basic

To add a user to an existing Windows NT security group, use the folowing Visual Basic code:

Dim Group as IADsGroup
Dim GroupName as String
Dim GroupDomain as String
Dim User as IADsUser
Dim UserName as String
Dim UserDomain as String
GroupName = "Target_Group_Name"
GroupDomain = "Target_Group_Domain"
UserName = "Target_User_Name"
UserDomain = "Target User Domain"
Set User = GetObject("WinNT://" & UserDomain & "/" & UserName & ",user")
Set Group = GetObject("WinNT://" & GroupDomain & "/" & GroupName & ",group")
Group.Add(User.ADsPath)Group.SetInfo

Removing Users from a Group

Not surprisingly, the IADsGroup interface also implements a method to remove users from a group. The Remove method follows a very similar syntax to the Add method of the IADsGroup interface:

Group.Remove(ADsPath of User Object)

Removing Users from a Group Using Visual Basic

To remove an existing group member from the bound group, use the following Visual Basic code:

Dim Group as IADsGroup
Dim GroupName as String
Dim GroupDomain as String
Dim User as IADsUser
Dim UserName as String
Dim UserDomain as String
GroupName = "Target_Group_Name"
GroupDomain = "Target_Group_Domain"
UserName = "Target_User_Name"
UserDomain = "Target User Domain"
Set User = GetObject("WinNT://" & UserDomain & "/" & UserName & ",user")
Set Group = GetObject("WinNT://" & GroupDomain & "/" & GroupName & ",group")Group.Remove(User.ADsPath)

Enumerating Members of a Group

Using User Manager, you can enumerate the members of a group in order to help you decide whether to add or remove an account to a particular group.

Enumerating Members of a Group Using Visual Basic

Using the following Visual Basic code, you can enumerate all users with membership in the bound security group:

Dim Group as IADsGroup
Dim GroupName as String
Dim GroupDomain as String
GroupName = "Target_Group_Name"
GroupDomain = "Target_Group_Domain"
Set Group = GetObject("WinNT://" & GroupDomain & "/" & GroupName & ",group")

For Each Member in Group.Members
   Debug.Print Member.Name
Next

Querying User Membership in a Group

The IsMember method will return a Boolean value indicating whether the user account passed as an argument belongs to the currently bound group. This is useful for positively verifying that a group addition action was completed successfully, or for testing a user's group membership before performing an action.

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Tip - By itself, the IsMember method simply returns a Boolean result, providing little value unless it is combined with a conditional to perform some action based upon the results of this test. This conditional may test to see if the user belongs to a specific group and then add the account if IsMember returns a false condition. You can also create a conditional to query if a user belongs to a specific administrative group before allowing the application to continue.

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Querying User Membership in a Group Using Visual Basic

Use the following Visual Basic code to verify that a user belongs to a specific security group:

Dim Group as IADsGroup
Dim GroupName as String
Dim GroupDomain as String
Dim User as IADsUser
Dim UserName as String
Dim UserDomain as String
GroupName = "Target_Group_Name"
GroupDomain = "Target_Group_Domain"
UserName = "Target_User_Name"
UserDomain = "Target_User_Domain"
Set User = GetObject("WinNT://" & UserDomain & "/" & UserName & ",user")
Set Group = GetObject("WinNT://" & GroupDomain & "/" & GroupName & ",group")
RetVal = Group.IsMember(User.ADsPath)Debug.Print RetVal

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Note - Notice that first the user account is bound and then the ADsPath of the user object is passed in to the IsMember method. This is done for two reasons. The first is simply that you want to make sure the account exists before attempting to verify group membership. Secondly, on non-domain controllers, unless the resource domain is explicitly specified, ADSI will return an incorrect result. The use of the ADsPath property as the argument to the IsMember method is the ideal way to accurately determine if a user belongs to a given security group.

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Note - When using the IsMember method to verify group membership, it is important to note that a False condition will be returned if a user's membership is enjoyed through global group membership. To prevent this, you may wish to examine the object class for each member of the group, bind to any global groups, and use the IsMember method at that level to verify group membership.

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Further Exploration: Using the IsMember Method to Control Rendering of Interface Elements in Active Server Pages

One of the most useful methods of the IADsGroup interface for the Web developer is the IsMember method. While many of the ADSI functions are only accessible by privileged user accounts, both privileged and non-privileged user accounts can receive a result from a call to the IsMember method.

For Web developers who frequently work with pages secured by Windows NT Challenge/Response or Basic Authentication, this property can enable some interesting enhancements to a Web interface. Although you can use other objects from Microsoft (such as PermChk) to perform similar duties, the IsMember method is an efficient and simple method for controlling the rendering of Web pages based on a user's group membership in a given SAM database.

Using the IsMember method in an Active Server Page, you can actually turn on and off interface elements based on a user's group membership. This can avoid the use of cookies, user preference databases, and can even prevent support calls when a user clicks a link to an item he or she does not have the proper permission to access.

Consider the following scenario to help illustrate the power of the IsMember method in Active Server Page (ASP) scripting:

The management team has determined that senior managers in the firm should be able to edit employee performance evaluations using a new intranet application. In an effort to keep the user interface as simple as possible, the intranet development team decides that the link enabling document editing should be available only to those users who actually have rights to edit the performance evaluation documents.

Using the IsMember method of the IADsGroup interface, the developer can simply query the SAM to find out whether the user is in the senior managers group, and render the link accordingly.

Unlike client-side script, ASPs will hide all conditionals and code used for generating the resulting HTML from user view. If the conditional evaluating the return value is False, the link simply will not show up in the client-side source code, and thus will not be rendered. The end result is a user interface that is tailored specifically to a user's actual permissions in the environment, providing greater simplicity and elegance in the interface implementation.

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Querying and Setting Group Description Field Values

In the SAM record of each local and global group, there exists an optional field that allows you to enter a description defining the function of the group. If you implement group descriptions using a meaningful naming standard (such as the owner of the group, the function of the group, or the name of the application served by the group), group description field queries can provide an especially powerful search mechanism when combined with ADSI's group enumeration methods.

Using the Description property of the IADsGroup interface, it is possible to query and set the value for the description field for any group.

Querying Group Description Field Value Using Visual Basic

Using Visual Basic, we can query the value of the description field using the following syntax:

Dim Group as IADsGroup
Dim GroupName as String
Dim GroupDomain as String
Dim RetVal as String
GroupDomain = "Target_Group_Domain"
GroupName = "Target_Group_Name"
Set Group = GetObject("WinNT://" & GroupDomain & "/" & GroupName & ",group")
RetVal = Group.DescriptionDebug.Print RetVal

Setting New Group Description Field Value Using Visual Basic

Just as you can query the value of the description field for any given group, you can also set a new value for the field programmatically.

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Tip - The ability to programmatically manipulate the description field can be useful for application setup routines that require a group to be created, or for appending information to an existing group description field.

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Use the following Visual Basic code to set a new value for the description field on a single group:

Dim Group as IADsGroup
Dim GroupName as String
Dim GroupDomain as String
Dim RetVal as String
GroupDomain = "Target_Group_Domain"
GroupName = "Target_Group_Name"
GroupDescription = "Target_Group_Description"
Set Group = GetObject("WinNT://" & GroupDomain & "/" & GroupName & ",group")
Group.Description = GroupDescriptionGroup.SetInfo

If you need to append the value of the description field to accommodate new information in your group description naming standard, simply perform a query of the current value, concatenate the old value with the amendment, and then write the new description back into the directory. This process is detailed as follows using Visual Basic:

Dim Group as IADsGroup
Dim OriginalValue as String
Dim ValueToAppend as String
Dim NewValue as String
Dim GroupName as String
Dim GroupDomain as String
Dim RetVal as String
GroupDomain = "Target_Group_Domain"
GroupName = "Target_Group_Name"
Set Group = GetObject("WinNT://" & GroupDomain & "/" & GroupName & ",group")
OriginalValue = Group.Description
ValueToAppend = " (Owner=NT Engineering)"
NewValue = OriginalValue & ValueToAppend
Group.Description = NewValueGroup.SetInfo

Enumerating Individual User Group Membership

Using User Manager, you have the ability not only to view all groups in a given domain, but you can also view the groups for which a specific user account has been assigned.

Although you have seen that the IADsGroup interface exposes the Members method to return all the users for a given group, you may also want to enumerate all groups for which a given user belongs. To perform this action, simply call upon the Groups method of the IADsUser interface to return a variant array containing all groups to which the specified user account belongs.

Enumerating Individual User Group Membership Using Visual Basic

To enumerate individual user group membership, you must first bind to the user account for which you seek group membership information. Following the binding, use a For...Each loop to step through each item in the collection returned by the call to the Groups method, as follows:

Dim User as IADsUser
Dim Group as IADsGroup
Dim UserDomain as String
Dim UserName as String
UserDomain = "Target_User_Domain"
UserName = "Target_User_Name"
Set User = GetObject("WinNT://" & UserDomain & "/" & User

Name & ",user")
For Each Group in User.Groups
   Debug.Print Group.NameNext