Uploading public keys
Pijul and the Nest use two kinds of keypairs (public and secret): keys for signing patches, and keys for SSH access.
SSH public keys
The Nest's profile settings page contains a field to add SSH public keys. At the moment, supported formats are Ed25519 and RSA. Pijul can handle password-protected keys, and can talk to SSH agents.
While you're here, you might as well setup a key to sign your patches. There is a really easy and fast procedure to do so, as explained here.