HAProxy dynamic server address based off of variable

[Phani Gopal Achanta]

 I want to dynamically route to a server by making use of a request
variable ssl_fc_sni.
Is it possible to configure haproxy server statement to use a variable for
server address and/or port?
Example
backend citest3bk_spice_default
       server compute1 %[ssl_fc_sni] ssl verify required crt server.pem
ca-file ca.pem force-tlsv12 weight 0

Currently, I get an error parsing [/etc/haproxy/haproxy.cfg:157] : 'server
compute1' : invalid address: '%[ssl_fc_sni]' in '%[ssl_fc_sni]'
I am running on Centos 7.5 with HAProxy 1.5.18
Thanks
Phani