composer.json

{
    "require": {
        "adoy/oauth2": "dev-master"
    }
}

submit-to-stash.php

<?php
// Load composer autoloader
require 'vendor/autoload.php';

const CLIENT_ID = 'xxx'; // OAuth 2.0 client_id
const CLIENT_SECRET = 'xxxx'; // OAuth 2.0 client_secret

const REDIRECT_URI = 'http://stashapi.local/submit-to-stash.php';
const AUTHORIZATION_ENDPOINT = 'https://www.deviantart.com/oauth2/draft15/authorize';
const TOKEN_ENDPOINT = 'https://www.deviantart.com/oauth2/draft15/token';
const SUBMIT_API = "https://www.deviantart.com/api/draft15/stash/submit";
const APPNAME = 'App.Name';

try {
    $client = new OAuth2\Client(CLIENT_ID, CLIENT_SECRET, OAuth2\Client::AUTH_TYPE_AUTHORIZATION_BASIC);
    if (!isset($_REQUEST['code'])) {
        $params = array('redirect_uri' => REDIRECT_URI);
        $auth_url = $client->getAuthenticationUrl(AUTHORIZATION_ENDPOINT, REDIRECT_URI);
        header('Location: ' . $auth_url);
        die('Redirecting ...');
    } else {
        $params = array('code' => $_REQUEST['code'], 'redirect_uri' => REDIRECT_URI);
        $response = $client->getAccessToken(TOKEN_ENDPOINT, OAuth2\Client::GRANT_TYPE_AUTH_CODE, $params);

        $val = (object) $response['result'];

        if (!$val->access_token) {
            throw new Exception("No access token returned: " . $val->human_error);
        }

        $client->setAccessToken($val->access_token);

        $client->setAccessTokenType(OAuth2\Client::ACCESS_TOKEN_OAUTH);
        
        $response = $client->fetch(
            SUBMIT_API,
            array(
                'title' => 'Fella Sample Image',
                'artist_comments' => 'Fella Sample Image',
                'keywords' => 'fella sample image',
                'folder' => APPNAME,
                'file' => "@fella.png"
            ),
            OAuth2\Client::HTTP_METHOD_POST
        );

        $result = (object) $response['result'];

        if (!$result) {
            throw new Exception('No valid JSON response returned');
        }
        
        if ($result->status == 'success') {
            print "Great Success! <a href=\"http://sta.sh/1{$result->stashid}\" target=\"_blank\">Stash ID {$result->stashid}</a>";
        } else {
            throw new Exception($result->human_error);
        }
    }
} catch (Exception $e) {
    print "Fatal Error: ".$e->getMessage();
}
?>