docker login registry1.dso.mil

Please advise if there is a better avenue for this.

Trying to login via docker CLI does not work with either username + password or "CLI secret"; in both cases I'm getting:

$ docker login registry1.dso.mil
Username: myusername
Password:
Error response from daemon: Get https://registry1.dso.mil/v2/: unauthorized: authentication required

Is there documentation on this somewhere?

Please help. Thanks!