What is the default method for users to authenticate with SSH without a password?

Key pair authentication is the default method for users to authenticate with SSH without a password. This method involves the use of a pair of cryptographic keys: a private key, which remains secure on the user's device, and a public key, which is placed in the remote server's authorized_keys file. When a user attempts to connect via SSH, the client presents the public key, and the server challenges it by sending a message encrypted with the public key. Only the matching private key can decrypt this message, thus validating the user's identity without the need for a password.

This approach is not only more secure than password authentication but also enables users to establish secure connections without entering a password every time. It reduces the risk associated with password exposure and is widely recommended in best security practices for SSH access.