Sanity Check: Can I do key based authentication with an RSA private key and a x509 cert on target?

Just as the title says, I'm trying to do a sanity check. I thought I couldI do key based authentication with an RSA private key and a x509 cert on target.

openssl req -x509 -nodes -days 3650 -newkey rsa:2048 -keyout id_rsa -out myCert.pem 

Dropped the .pem on the remote server (Axway) for SFTP connections. Getting the following in debug output for SFTP:

debug2: key_type_from_name: unknown key type '-----BEGIN'

debug2: key_type_from_name: unknown key type 'Proc-Type:'

debug2: key_type_from_name: unknown key type 'DEK-Info:'

debug2: key_type_from_name: unknown key type '-----END'

debug1: identity file /home/username/.ssh/id_rsa type -1

Am I missing something or am I totally off that I can't do key auth with x509?