Authenticate a domain

**This endpoint allows you to authenticate a domain.** If you are authenticating a domain for a subuser, you have two options: 1. Use the "username" parameter. This allows you to authenticate a domain on behalf of your subuser. This means the subuser is able to see and modify the authenticated domain. 2. Use the Association workflow (see Associate Domain section). This allows you to authenticate a domain created by the parent to a subuser. This means the subuser will default to the assigned ...