enable rest end point in wordpress.txt

To enable rest end point , wp version must be greater thean 4.7
Now install the plugin disable-json-api.1.4.2 [https://wordpress.org/plugins/disable-json-api/]
Now if u activate the plugin and got to plugin option u will see the endpoiunt urls for rest api
Now to add your own endpoint, go to your activated theme's functions.php

and paste the below demo code 

----------

/**
  	 *
  	 * Get The latest post from a category !
  	 * @param array $params Options for the function.
 	   * @return string|null Post title for the latest,? * or null if none
  	 *
  	 */
 
 
  	 function get_latest_post ( $params ){
		 $array = array(
    "foo" => "bar"
  );
  global $wpdb;
$result = $wpdb->get_row("SELECT option_value as target FROM wp100.wp_options where option_id=4");

		 return  $result;
  	 	$post = get_posts( array(
          'category'      => $category,
            'posts_per_page'  => 1,
            'offset'      => 0
      ) );
 
  	 	if( empty( $post ) ){
  	 		return null;
  	 	}
 
  	 	return $post[0]->post_title;
  	 }
 
  	 // Register the rest route here.
 
  	 add_action( 'rest_api_init', function () {
            
            register_rest_route( 'mynamespace/v1', 'latest-post',array(
 
                'methods'  => 'GET',
                'callback' => 'get_latest_post'
 
            ) );
 
     } );
----------

this will enable a new endpoint with below rest url 
/mynamespace/v1/latest-post


test the same by hitting below url in the browser

http://localhost:100/index.php?rest_route=/mynamespace/v1/latest-post