On the WWDC18 Apple presented the support for EWS/Exchange on macOS Mojave. Would be great to see this feature soon in Meraki. The workaround at the moment should go with custom profile, but I haven't tried it at the moment. If someone has experienced already with the custom profile, please share your knowledge, specially how to go with username/password when authenticating with AD.
macOS MDM references page
https://help.apple.com/deployment/macos/#/ior1c8a0c6f4