Retrieving IPsec VPN PSK key from Fortigate

The API entry point is ;

"https://x.x.x.x/api/v2/cmdb/vpn.ipsec/phase1-interface?plain-text-password=1?

The full http get would look like the following ;

curl -k -H "Authorization: rest_api_admin_user zw7q8QyGrHwtfrn8tkGyfNbnGGN7js" "https://192.168.1.99/api/v2/cmdb/vpn.ipsec/phase1-interface?plain-text-password=1?access_token=zw7q8QyGrHwtfrn8tkGyfNbnGGN7js"

The output and field for "psksecret": will show the text value. 

Account with API permissions is must

Ken Felix Security Blog: fortios how to recover ipsec-vpn PSK string in text format (socpuppet.blogspot.com)