There's also dl, which supports creating single use links for third parties to upload files: https://www.thregr.org/~wavexx/software/dl/
Host *
# Disable SSHv1
RSAAuthentication no
# Only use a key explicitely provided by an IdentityFile directive
IdentitiesOnly yes
# %h expands to the hostname, and %u to the username
IdentityFile ~/.ssh/%h/%u.key
This ensures that at most one key is used, and prevents me from having to modify my config every time I generate a key for a new host.