"web-authentication https" not supported on SRX300 running 15.1X49-D70.3?

me@co-firewall# show interfaces ge-0/0/5 unit 0 family inet address aa.bb.cc.dd/29    
##
## Warning: statement ignored: unsupported platform (srx300)
##
web-authentication https;

[edit]
me@co-firewall# run show version 
Hostname: co-firewall
Model: srx300
Junos: 15.1X49-D70.3
JUNOS Software Release [15.1X49-D70.3]

I am sure this feature was working before I upgraded to 15.1X49-D70.3 from 15.1X49-D45.

This page says it should be supported:

https://www.juniper.net/techpubs/en_US/junos/topics/reference/configuration-statement/interfaces-edit-web-authentication.html

Did I miss something? Thanks.