How do I login to SQL Server via group membership in another domain When attempting to connect to SQL Server (2012), I get a login failed error message. The error log on the server reports:

Logon        Error: 18456, Severity: 14, State: 5.
Logon        Login failed for user 'MYDOMAIN\mswart'. Reason: Could not find a login matching the name provided. [CLIENT: 192.168.---.--]


However, I expected to be able to login based on my membership to a group MYDOMAIN\MYTEAM

I'm able to login when MYDOMAIN\mswart is created as a login.

The SQL Server machine has joined domain OTHERDOMAIN and the SQL Server service account is also a member of OTHERDOMAIN.

Maybe I'm not looking at the right thing. I'm looking for troubleshooting steps I can take to narrow down the issue so I can understand why I can't log in.

Aaron Bertrand's post Troubleshooting Error 18456 was almost useful... in the comments, it looks like a Gary Mazzone experienced the same issue.
In my case I was able to narrow down my trouble by working with my sysadmin about how the group was defined.

Knowing that the SQL Server was hosted on a machine that had joined another domain and was running with a user account on that other domain, we looked at the Group Scopes in active directory.

My user could authenticate properly after the scope was changed to universal. 

If I find an authoritative source on SQL Server's behavior with respect to these domain group types, I'll be sure to update this answer.