admin-options.php

<?php
add_action( 'admin_menu', 'api_connector_admin_add_page' );
function api_connector_admin_add_page() {
	add_options_page( 'API Connector', 'API Connector', 'manage_options', 'api_connector', 'api_connector_settings_page' );
}

function api_connector_settings_page() {
	require_once API_CONNECTOR_ABSPATH . 'templates/settings.php';
}

add_action( 'admin_init', 'api_connector_register_settings' );
function api_connector_register_settings() {
	$option_group = 'api_connector';
	$option_prefix = 'api_connector_';
	register_setting( $option_group, $option_prefix . 'auth_url' );
	register_setting( $option_group, $option_prefix . 'base_url' );
	register_setting( $option_group, $option_prefix . 'grant_type' );
	register_setting( $option_group, $option_prefix . 'refresh_token' );

	// settings for client credentials grant type API requests
	register_setting( $option_group, $option_prefix . 'grant_client_credentials_client_id' );
	register_setting( $option_group, $option_prefix . 'grant_client_credentials_client_secret' );

	// settings for password grant type API requests
	register_setting( $option_group, $option_prefix . 'grant_password_client_id' );
	register_setting( $option_group, $option_prefix . 'grant_password_client_secret' );
	register_setting( $option_group, $option_prefix . 'grant_password_username' );
	register_setting( $option_group, $option_prefix . 'grant_password_password' );
}

add_action( 'admin_enqueue_scripts', 'api_connector_enqueue_scripts' );
function api_connector_enqueue_scripts( $hook ) {
	if ( 'settings_page_api_connector' == $hook ) {
		wp_enqueue_style( 'api-connector-css', plugins_url( 'assets/css/style.css', __FILE__ ) );
		wp_enqueue_script( 'api-connector-js',  plugins_url( 'assets/js/main.js', __FILE__ ), array( 'jquery' ), false, true );
	}
}