Twitter application-only authentication to connect and retrieve a bearer token.

2018-04-09-twitter-api-connect.php

<?php

/**
 * Application-only authentication
 *
 * Application-only authentication is a form of authentication where an
 * application makes API requests on its own behalf, without the user context.
 * This method is for developers that just need to access public information.
 *
 * developer.twitter.com/en/docs/basics/authentication/overview/application-only
 *
 */
function api_twitter_connect()
{
    /**
     * Consumer Keys & Secret
     */
    $key = 'xxxxxxxxxxxxxxxx';
    $sec = 'xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx';

    /**
     * Encode keys according to RFC 1738
     */
    $enc_key = urlencode($key);
    $enc_sec = urlencode($sec);

    /**
     * Base64 encoded bearer token credentials
     */
    $credential = base64_encode($enc_key.':'.$enc_sec);

    /**
     * Create cURL session to Twitter oauth2/token URL & return cURL handle
     */
    $ch = curl_init('https://api.twitter.com/oauth2/token');

    /**
     * Set cURL options & create header request
     *
     * The request must be a HTTP POST request.
     * The request must include an Authorization header with the value of
     * Basic <base64 encoded value>.
     * The request must include a Content-Type header with the value of
     * application/x-www-form-urlencoded;charset=UTF-8.
     * The body of the request must be grant_type=client_credentials.
     */
    curl_setopt_array($ch, [
        //set curl timeout
        CURLOPT_TIMEOUT => 20,
        //set a custom user-agent
        CURLOPT_USERAGENT => 'MyAwesome Twitter App 1.0',
        //create the header request with credentials
        CURLOPT_HTTPHEADER => [
            'Authorization: Basic '.$credential,
            'Content-Type: application/x-www-form-urlencoded;charset=UTF-8',
            'Accept-Encoding: gzip'
        ],
        //set body of the request
        CURLOPT_POSTFIELDS => 'grant_type=client_credentials',
        //return transfer as string, instead of outputting directly
        CURLOPT_RETURNTRANSFER => true,
        //leaving CURLOPT_ENCODING empty allows uncompressing
        CURLOPT_ENCODING => '',
    ]);

    /**
     * Return false if error
     */
    if (!$request = curl_exec($ch)) {
        return false;
    }

    /**
     * Decode the JSON response
     */
    $token = json_decode($request);

    /**
     * free request data
     */
    unset($request);

    /**
     * close cURL resource
     */
    curl_close($ch);

    /**
     * use token to make request
     */
    return $token;
}

?>