Add member to AD group from a trusted domain

I have two domains, in a trusted relationship, that I'm trying to manage from a C# web application. To do that, I have to impersonate two different technical users, but that works good, so I will not emphasize that part of the code.

To build proper and easy to manage ACLs for the file system, I must

• Create a group in domainA (OK!)
• Find a user in domainB (OK!)
• Add the user to the group (FAILS when committing changes, error message: There is no such object on the server. (Exception from HRESULT: 0x80072030))

If I'm adding a user from the same domain, the code works perfectly, so I believe I'm only missing a small partial info here. I used this document as a reference and saw this question as well (and a few more citing this error message) but neither of them helped.

Code (try-catch block removed to make it simpler)

// de is a DirectoryEntry object of the AD group, received by the method as a parameter
// first impersonation to search in domainB
// works all right
if (impersonator.impersonateUser("techUser1", "domainB", "pass")) {
    DirectoryEntry dom = new DirectoryEntry("LDAP://domainB.company.com/OU=MyOU,DC=domainB,DC=company,DC=com", "techUser1", "pass");
    de.Invoke("Add", new object[] { "LDAP://domainB.company.com/CN=theUserIWantToAdd,OU=MyOU,DC=domainB,DC=company,DC=com" });
    // de.Invoke("Add", new object[] { "LDAP://domainA.company.com/CN=anotherUserFromDomainA,OU=AnotherOU,DC=domainB,DC=company,DC=com" });
    impersonator.undoImpersonation();
}

// second impersonation because the group (de) is in domainA
// and techUser2 has account operator privileges there
if (impersonator.impersonateUser("techUser2", "domainA", "pass"))
{
    de.CommitChanges();
    impersonator.undoImpersonation();
    return true;
}
else
{
    // second impersonation was unsuccessful, so return an empty object
    return false;
}

Line 6 works, if I debug it or force the properties to be written to HttpResponse, it is clearly there. So the LDAP queries seem to be OK.

Also, if I comment out line 6 and uncomment 7, so basically I add a user from the same domain, the whole thing works miraculously. With domainB, I'm stuck. Any good piece of advice?

Following your code, I see that you're getting de as a parameter, which is in Domain A. Then you're creating DirectoryEntry object dom, which is getting impersonated, but never getting used. However, you're trying to add an object from Domain B to de directly using LDAP. This line:

de.Invoke("Add", new object[{"LDAP://domainB.company.com/CN=theUserIWantToAdd,OU=MyOU,DC=domainB,DC=company,DC=com" }); 

is not getting impersonated.

Assuming your impersonation works correctly, use dom object which is already impersonated with DirectorySearcher to find the user in Domain B and then add the user object from Domain B to de.

...
using (DirectoryEntry dom = new DirectoryEntry("LDAP://domainB.company.com/OU=MyOU,DC=domainB,DC=company,DC=com", "techUser1", "pass"))
{
    using (DirectorySearcher searcher = new DirectorySearcher(dom))
    {
        searcher.Filter = "(&(objectClass=user)(CN=theUserIWantToAdd))";
        SearchResult result = searcher.FindOne();
        de.Invoke("Add", new object[] { result.Path });
    }
}
...

UDPATE

This example will show you how to get user SID from one domain, search group from another domain and add user to group using SID.

//GET THE USER FROM DOMAIN B
using (UserPrincipal userPrincipal = UserPrincipal.FindByIdentity(domainContext, UPN))
{
    if (userPrincipal != null)
    {
       //FIND THE GROUP IN DOMAIN A
       using (GroupPrincipal groupPrincipal = GroupPrincipal.FindByIdentity(domainContext, groupName))
       {
          if (groupPrincipal != null)
          {
             //CHECK TO MAKE SURE USER IS NOT IN THAT GROUP
             if (!userPrincipal.IsMemberOf(groupPrincipal))
             {
                string userSid = string.Format("<SID={0}>", userPrincipal.SID.ToString());
                DirectoryEntry groupDirectoryEntry = (DirectoryEntry)groupPrincipal.GetUnderlyingObject();
                groupDirectoryEntry.Properties["member"].Add(userSid);
                groupDirectoryEntry.CommitChanges();
              }
           }
        }
     }
 }

Please note that I skipped all the impersonation in the above code.