Windows – Add an account from a trusted domain to Domain Admins

Our domain is trusting an external domain (not in the same forest) and we need to add a group from the external domain into the Domain Admins group of our domain.

I understand that the Domain Admins group is a global group, so we cannot add groups from other domains into it. But I have seen several workarounds on the internet, but none of these seem to work in our situation.

I tried creating a universal group and a domain local group, but I cannot add either of these to the Domain Admins group and only the domain Local groups lets me add accounts from the external trusted domain.

• Global security group (e.g. Domain Admins)

  • Can add Domain Local group: No
  • Can add Global group: Yes
  • Can add Universal group: No
  • Can add from trusted domain: No

• Universal security group (e.g. Enterprise Admins)

  • Can add Domain Local group: No
  • Can add Global group: Yes
  • Can add Universal group: Yes
  • Can add from trusted domain: No

• Domain Local security group (e.g. Administrators)

  • Can add Domain Local group: Yes
  • Can add Global group: Yes
  • Can add Universal group: Yes
  • Can add from trusted domain: Yes

               |      Group can contain members of type                 |
| Group type   | Global | Universal | Domain local | Trusted Foreigners |
|--------------|--------|-----------|--------------|--------------------|
| Global       | Yes    |           |              |                    |
| Universal    | Yes    | Yes       |              |                    |
| Domain local | Yes    | Yes       |              | Yes                |

The Global Domain Admins group can only contain other Global groups.

And Global groups cannot seems to directly (or indirectly) contain principles from foreign domains.

Workaround

How can I add a group to the Administrators group on every machine in the domain?

Cannot work; a Domain local group cannot contain other Domain local groups.

The only workaround i can see is manually create duplicate accounts for every user in the local domain

Cons: decreased network security, lower user productivity, complicates administration, worse administrative control, inconsistent policies, increased TCO.

Bonus Chatter

From Application Specification for Microsoft Windows Server,
Chapter 5. Security Services:

Single Sign-On (SSO) allows enterprise network users to seamlessly
access all authorized network resources, on the basis of a single
authentication that is performed when they initially access the
network. SSO can improve the productivity of network users, reduce the
cost of network operations, and improve network security.

• Better network security. All SSO methods available under Windows
  provide secure authentication and provide a basis for encrypting the
  user's session with the network resource. Eliminating multiple
  passwords also reduces a common source of security breaches – users
  writing down their passwords.

• Improved user productivity. Users are no longer required to remember
  multiple logons, nor are they required to remember multiple passwords
  in order to access network resources. This is also a benefit to help
  desk personnel, who need to field fewer requests for forgotten
  passwords.

• Simpler administration. SSO-related tasks are performed
  transparently as part of normal maintenance, using the same tools that
  are used for other administrative tasks.

• Better administrative control. All SSO-specific information is
  stored in a single repository, the Active Directory. Because there is
  a single, authoritative listing of each user's rights and privileges,
  the administrator can change a user's privileges and know that the
  results will propagate network wide.

• Consolidation of heterogeneous networks. By joining disparate
  networks, administrative efforts can be consolidated, ensuring that
  administrative best practices and corporate security policies are
  being consistently enforced.

Bonus Reading

• Group scope (archive)