vyos@r1-1.3# set vpn ipsec site-to-site peer 100.64.0.2 authentication pre-shared-secret 
Possible completions:
   <text>       Pre-shared secret key

Detailed information:
  
  Use of single quotes to set pre-shared secret key is recommended.  If you are
  using special characters in the pre-shared scret key then single quotes are
  required.