-cert: specify an SSH certificate
The -cert option allows you to specify the name of a certificate file containing a signed version of your public key. If you specify this option, PuTTY will present that certificate in place of the plain public key, whenever it tries to authenticate with a key that matches. (This applies whether the key is stored in Pageant or loaded directly from a file by PuTTY.)
This option is equivalent to the ‘Certificate to use with the private key’ box in the Auth panel of the PuTTY configuration box (see section 4.22.2).