While webshells are nice, it'd be nice to be able to login directly. To do so, please add your own public key to ~/.ssh/authorized_keys, using the webshell. Make sure to copy it correctly! The key is in the ssh banner, displayed when you login remotely with ssh, to shell2017.picoctf.com
There are plenty of tutorials out there. This one covers key generation: https://confluence.atlassian.com/bitbucketserver/creating-ssh-keys-776639788.html
Then, use the web shell to copy/paste it, and use the appropriate tool to ssh to the server using your key
The sad part is that I finished the Master Challenge of this level before I finished this one. Just because I kept making 'authorized_keys' a directory, instead of a file. Eventually, I figured it out enough to connect and get the flag. What I did was I pico'd a file called 'authorized_keys' and put my public key in there.