There is no limit to the number of domains you can login to, the limit is 3 logins per minute for each admin to a specific domain.
I logged in once to each domain, after MDS - CMA1 - CMA2 succeeded, CMA3, CMA4 ... was denied.
Please consider making this a variable, not a hard limit.
The login-to-domain API functionality is similar to SmartConsole where you can login to a domain from the MDS level, a new SmartConsole opens to the domain while the SmartConsole to the MDS level remains open. We will improve the documentation to make it more clear.
Thanks for clarifying this; now that I understand the concept I will use it when working on multiple CMAs.
Regarding your use case, in future Jumbo Hotfixes, there will be an option to show policy packages of all domains from the MDS level and login to all domains will not be needed.
That was just an example on what I wanted to achieve. Though it is good to have visibility from the MDS level.