On a aws server, you need to connect via EC2-USER and then perform switch user to connect Oracle user.
Use below commands to allow Oracle user connect the aws EC2 server remotely
Connect EC2 server
Connect to your ec2 server with ec2-user and switch to oracle user and make .ssh directory to hold remote authentication key
su - oracle mkdir .ssh chmod 700 .ssh
Add remote authentication
Below commands will add remote authentication to oracle user
touch .ssh/authorized_keys chmod 600 .ssh/authorized_keys GET http://169.254.169.254/latest/meta-data/public-keys/0/openssh-key>.ssh/authorized_keys
Now you must be able to login to EC2 server via putty directly with Oracle user!