wp_ajax_install_plugin

function wp_ajax_install_plugin() {
	check_ajax_referer( 'updates' );

	if ( empty( $_POST['slug'] ) ) {
		wp_send_json_error(
			array(
				'slug'         => '',
				'errorCode'    => 'no_plugin_specified',
				'errorMessage' => __( 'No plugin specified.' ),
			)
		);
	}

	$status = array(
		'install' => 'plugin',
		'slug'    => sanitize_key( wp_unslash( $_POST['slug'] ) ),
	);

	if ( ! current_user_can( 'install_plugins' ) ) {
		$status['errorMessage'] = __( 'Sorry, you are not allowed to install plugins on this site.' );
		wp_send_json_error( $status );
	}

	require_once ABSPATH . 'wp-admin/includes/class-wp-upgrader.php';
	include_once ABSPATH . 'wp-admin/includes/plugin-install.php';

	$api = plugins_api(
		'plugin_information',
		array(
			'slug'   => sanitize_key( wp_unslash( $_POST['slug'] ) ),
			'fields' => array(
				'sections' => false,
			),
		)
	);

	if ( is_wp_error( $api ) ) {
		$status['errorMessage'] = $api->get_error_message();
		wp_send_json_error( $status );
	}

	$status['pluginName'] = $api->name;

	$skin     = new WP_Ajax_Upgrader_Skin();
	$upgrader = new Plugin_Upgrader( $skin );
	$result   = $upgrader->install( $api->download_link );

	if ( defined( 'WP_DEBUG' ) && WP_DEBUG ) {
		$status['debug'] = $skin->get_upgrade_messages();
	}

	if ( is_wp_error( $result ) ) {
		$status['errorCode']    = $result->get_error_code();
		$status['errorMessage'] = $result->get_error_message();
		wp_send_json_error( $status );
	} elseif ( is_wp_error( $skin->result ) ) {
		$status['errorCode']    = $skin->result->get_error_code();
		$status['errorMessage'] = $skin->result->get_error_message();
		wp_send_json_error( $status );
	} elseif ( $skin->get_errors()->has_errors() ) {
		$status['errorMessage'] = $skin->get_error_messages();
		wp_send_json_error( $status );
	} elseif ( is_null( $result ) ) {
		global $wp_filesystem;

		$status['errorCode']    = 'unable_to_connect_to_filesystem';
		$status['errorMessage'] = __( 'Unable to connect to the filesystem. Please confirm your credentials.' );

		// Pass through the error from WP_Filesystem if one was raised.
		if ( $wp_filesystem instanceof WP_Filesystem_Base && is_wp_error( $wp_filesystem->errors ) && $wp_filesystem->errors->has_errors() ) {
			$status['errorMessage'] = esc_html( $wp_filesystem->errors->get_error_message() );
		}

		wp_send_json_error( $status );
	}

	$install_status = install_plugin_install_status( $api );
	$pagenow        = isset( $_POST['pagenow'] ) ? sanitize_key( $_POST['pagenow'] ) : '';

	// If installation request is coming from import page, do not return network activation link.
	$plugins_url = ( 'import' === $pagenow ) ? admin_url( 'plugins.php' ) : network_admin_url( 'plugins.php' );

	if ( current_user_can( 'activate_plugin', $install_status['file'] ) && is_plugin_inactive( $install_status['file'] ) ) {
		$status['activateUrl'] = add_query_arg(
			array(
				'_wpnonce' => wp_create_nonce( 'activate-plugin_' . $install_status['file'] ),
				'action'   => 'activate',
				'plugin'   => $install_status['file'],
			),
			$plugins_url
		);
	}

	if ( is_multisite() && current_user_can( 'manage_network_plugins' ) && 'import' !== $pagenow ) {
		$status['activateUrl'] = add_query_arg( array( 'networkwide' => 1 ), $status['activateUrl'] );
	}

	wp_send_json_success( $status );
}