Matthias,
As you have seen, XOS does not directly support .1x, MAC and STP on a port at the same time. We can workaround this by creating a carrier vlan and adding ports tagged to the vlan. Here is an example:
# Create VLAN for Carrier - Add all user ports to this VLAN
#
create vlan FAKE_EDGE_MSTP tag 4051 (tag could be any...)
configure FAKE_EDGE_MSTP add port (user port listing) tag
#
# STP Configuration - Will turn on
#
configure s0 delete vlan default port all
disable s0 auto-bind vlan default
configure s0 mode mstp cist
configure s0 priority 0
create stpd fake_stm
configure fake_stm mode mstp msti 1
configure fake_stm priority 01
configure fake_stm add vlan FAKE_EDGE_MSTP port (user port listing) dot1d
configure s0 ports link-type edge (user port listing) edge-safeguard enable bpdu-restrict
configure fake_stm ports link-type edge (user port listing) edge-safeguard enable bpdu-restrict
en fake_stm
en s0
en stp
#
Bill