What about Trusted Access?
https://documentation.meraki.com/General_Administration/Cross-Platform_Content/Trusted_Access_for_Se...
It uses Systems Manager, but in this configuration, it does not manage the phone. The agent installs the certificate on the phone to simplify the process for the user and administrator.
Failing that, you could look at some cloud-based RADIUS solutions. I haven't done this myself and don't know if this is a workable solution, but Jump Cloud is popular.
https://jumpcloud.com/
You could also check out Splash Access solutions.
https://www.splashaccess.com/