Create the post on wordpress.com site using oAuth and Rest API. I have created the posts on https://maheshwaghmare.wordpress.com/?p=4034 using below code.

create-post-on-wordpress-com.php

<?php
/**
 * Create a post on your site WordPress.com using Rest API (oAuth).
 * I have created the posts on https://maheshwaghmare.wordpress.com/ using below code.
 *
 * > How it works?
 * Using below two fucntion `get_access_key()` and `create_post()` create the post on https://wordpress.com/
 *
 * Function `get_access_key()` get the `access_key` by passing authentication details.
 * Function `create_post()` create a post by passing `access_key` and `post arguments`.
 */

// Step: 1  Add authentication details to get auth key.
$auth_args = array(
	'username'      => '',
	'password'      => '',
	'client_id'     => '',
	'client_secret' => '',
	'grant_type'    => 'password', // Keep this as it is.
);

$access_key = get_access_key( $auth_args );

// Step: 2  Set post arguments and pass it create the post.
$post_args = array(
	'title'       => 'Hello APAI World',
	'content'     => 'Hello. I am a test post. I was created by the API',
	'tags'        => 'tests',
	'post_status' => 'draft',
	'categories'  => 'API',
);

// Create a post with the access key.
create_post( $access_key, $post_args );







/**
 * Create post with access key.
 * 
 * @param  string $access_key 	Access key.
 * @param  array $post_args 	Post arguments.
 * @return mixed       			Post response.
 */
function create_post( $access_key, $post_args )
{
	$options  = array (
		'http' => array(
			'ignore_errors' => true,
			'method'        => 'POST',
			'header'        => array(
		    	0 => 'authorization: Bearer ' . $access_key,
		    	1 => 'Content-Type: application/x-www-form-urlencoded',
		  	),
		  	'content' => http_build_query( $post_args ),
		),
	);
	 
	$context  = stream_context_create( $options );

	$response = file_get_contents(
	    'https://public-api.wordpress.com/rest/v1/sites/YOURSITEID/posts/new/',
	    false,
	    $context
	);
	return json_decode( $response );
}

/**
 * Get Access Key.
 * 
 * @param  array $args 	Auth arguments.
 * @return mixed       	Auth response.
 */
function get_access_key( $args ) {

	// Access Token.
	$curl = curl_init( 'https://public-api.wordpress.com/oauth2/token' );
	curl_setopt( $curl, CURLOPT_POST, true );
	curl_setopt( $curl, CURLOPT_POSTFIELDS, $args );
	curl_setopt( $curl, CURLOPT_RETURNTRANSFER, 1);

	$auth = curl_exec( $curl );

	$auth = json_decode($auth);

	// Access Key.
	return $auth->access_token;
}