Source

File: wp-admin/includes/class-wp-filesystem-ssh2.php

public function __construct( $opt = '' ) {
		$this->method = 'ssh2';
		$this->errors = new WP_Error();

		// Check if possible to use ssh2 functions.
		if ( ! extension_loaded( 'ssh2' ) ) {
			$this->errors->add( 'no_ssh2_ext', __( 'The ssh2 PHP extension is not available' ) );
			return;
		}

		// Set defaults:
		if ( empty( $opt['port'] ) ) {
			$this->options['port'] = 22;
		} else {
			$this->options['port'] = $opt['port'];
		}

		if ( empty( $opt['hostname'] ) ) {
			$this->errors->add( 'empty_hostname', __( 'SSH2 hostname is required' ) );
		} else {
			$this->options['hostname'] = $opt['hostname'];
		}

		// Check if the options provided are OK.
		if ( ! empty( $opt['public_key'] ) && ! empty( $opt['private_key'] ) ) {
			$this->options['public_key']  = $opt['public_key'];
			$this->options['private_key'] = $opt['private_key'];

			$this->options['hostkey'] = array( 'hostkey' => 'ssh-rsa' );

			$this->keys = true;
		} elseif ( empty( $opt['username'] ) ) {
			$this->errors->add( 'empty_username', __( 'SSH2 username is required' ) );
		}

		if ( ! empty( $opt['username'] ) ) {
			$this->options['username'] = $opt['username'];
		}

		if ( empty( $opt['password'] ) ) {
			// Password can be blank if we are using keys.
			if ( ! $this->keys ) {
				$this->errors->add( 'empty_password', __( 'SSH2 password is required' ) );
			}
		} else {
			$this->options['password'] = $opt['password'];
		}
	}