What are the supported authentication options for the ME APs? Do they support only login through local credentials or RADIUS/TACACS+ is also supported?
If you mean host to network attachment, then it works much like any other Cisco wireless products using WPA2 Personal (Pre-Shared Key) or WPA2 Enterprise (802.1X using RADIUS).
If you mean logging into the controller, it is very much like any other Cisco device, and you can use AAA with RADIUS or TACACS+.
Cisco maintains a full library of documentation for its products, including things like, Cisco Mobility Express Deployment Guide.