With autonomous hardware you don't have alot of options. You can have a different SSID on each radio that maps to the same VLAN(or untagged) but if you want to have two SSID's you either need to use regular VLAN mapping or MBSSID's which still require multiple VLANs.
There's really just no point in running two SSID's mapping to the same network. You can use 2.4ghz for one and 5ghz for the other, or use a second AP.
Sure you could probably use radius AAA override but now you're way overcomplicating something that should be simple. Let us know your objective and we can help.