I like to use the WordPress native methods when I can, here's my take on oAuth. The examples below retrieves the access token


Facebook

<br />
&lt;?php<br />
define('FACEBOOK_APPID','123'); // replace 123 with your app id<br />
define('FACEBOOK_APPSECRET','abc'); // replace abc with your app secret<br />
define('REDIRECTURI','http://your.redirect.url');</p>
<p>if ($_GET['code'] != '') {<br />
	if ($_GET['state'] != '' &amp;&amp; wp_verify_nonce($_GET['state'], 'my-nonce')) {</p>
<p>		$api_url = sprintf(&quot;https://graph.facebook.com/oauth/access_token?client_id=%s&amp;redirect_uri=%s&amp;client_secret=%s&amp;code=%s&quot;,<br />
			urlencode(FACEBOOK_APPID),<br />
			urlencode(REDIRECTURI),<br />
			urlencode(FACEBOOK_APPSECRET),<br />
			urlencode($_GET['code'])<br />
		);</p>
<p>		$response = wp_remote_request($api_url, array(<br />
			'timeout' =&gt; 60,<br />
			'sslverify' =&gt; false,<br />
			'method' =&gt; 'GET'<br />
		));</p>
<p>		if( is_wp_error( $response ) ) {<br />
		   echo 'ERROR';<br />
		} else {<br />
			$args = wp_parse_args( wp_remote_retrieve_body($response), array() );<br />
			echo $args['access_token'];<br />
		}<br />
	}<br />
} else {<br />
     $facebook_dialog_url = sprintf(&quot;https://www.facebook.com/dialog/oauth?client_id=%s&amp;redirect_uri=%s&amp;state=%s&quot;,<br />
     	FACEBOOK_APPID,<br />
     	urlencode(REDIRECTURI),<br />
     	wp_create_nonce ('my-nonce')<br />
     );</p>
<p>	echo '&lt;a href=&quot;'. $facebook_dialog_url .'&quot;&gt;LOGIN TO FACEBOOK&lt;/a&gt; &lt;br /&gt;';<br />
}<br />
?&gt;<br />

GitHub

<br />
&lt;?php<br />
define('GIST_CLIENTID','123'); // replace 123 with your client id<br />
define('GIST_CLIENTSECRET','abc'); // replace abc with your client secret<br />
define('REDIRECTURI','http://your.redirect.url');</p>
<p>if ($_GET['code'] != '') {<br />
	$response = wp_remote_request('https://github.com/login/oauth/access_token', array(<br />
		'method' =&gt; 'POST',<br />
		'timeout' =&gt; 60,<br />
		'sslverify' =&gt; false,<br />
		'body' =&gt;  array(<br />
			'client_id' =&gt; GIST_CLIENTID,<br />
			'client_secret' =&gt; GIST_CLIENTSECRET,<br />
			'code' =&gt; $_GET['code'],<br />
			'redirect_uri' =&gt; REDIRECTURI<br />
		)<br />
	));</p>
<p>	if (is_wp_error( $response )) {<br />
	   echo 'Something went wrong! &lt;br /&gt;';<br />
	} else {<br />
		$args = wp_parse_args( wp_remote_retrieve_body($response), array() );<br />
		echo $args['access_token'];<br />
	}<br />
} else {<br />
	$gist_dialog_url =   sprintf(&quot;https://github.com/login/oauth/authorize?client_id=%s&amp;redirect_uri=%s&quot;,<br />
		GIST_CLIENTID,<br />
		urlencode(REDIRECTURI)<br />
	);<br />
	echo '&lt;a href=&quot;'. $gist_dialog_url .'&quot;&gt;LOGIN IN TO GIST (GITHUB)&lt;/a&gt; &lt;br /&gt;';<br />
}<br />
?&gt;<br />

.. more will be added when I get time to play with other services and their oAuth implementation.