Tracking visits from LinkedIn - php

Question

I use LinkedIn and other Social Media to promote certain blog content on my Website. My website is on Wordpress and I therefore wrote a Plugin that created a widget for displaying the visit source. Once I have this source, I can store this on a table and can view the number of visits from each Social Media channel to test the effectiveness of the post.
The problem is that while I can identify click throughs from Facebook, Twitter, G+ etc. with no problem, I do not get any referer information from LinkedIn.
I use the read the information as follows:
//Get the referer from Wordpress
$ref_raw = wp_get_raw_referer();
echo '<li>RAW: '.( strlen($ref_raw)? $ref_raw: 'None' ).'</li>';
//Get the IP from the server to check
$ref_srv = $_SERVER['HTTP_REFERER'];
echo '<li>PHP: '.( strlen($ref_srv)? $ref_srv: 'None' ).'</li>';
//Get other information
$ip = strlen($_SERVER["HTTP_X_REAL_IP"])? $_SERVER["HTTP_X_REAL_IP"]: $_SERVER['REMOTE_ADDR'];
echo '<li>REFERRER IP: '.( strlen($ip)? $ip: 'None' ).'</li>';
$agent = isset($_SERVER['HTTP_USER_AGENT'])&& strlen($_SERVER['HTTP_USER_AGENT'])? $_SERVER['HTTP_USER_AGENT']: '';
echo '<li>USER AGENT: '.( strlen($agent)? $agent: 'None' ).'</li>';
echo '<li>URI: '.$_SERVER['REQUEST_URI'].'</li>';
The output from this code when a visit originated from Facebook is as follows:
RAW: https://www.facebook.com/ PHP: https://www.facebook.com/
REFERRER IP: 89.127.12.32
USER AGENT: Mozilla/5.0 (Windows NT 10.0; Win64; x64)
AppleWebKit/537.36 (KHTML, like Gecko) Chrome/71.0.3578.98 Safari/537.36 REFERRAL
URI: /how-speed-affects-your-website/?fbclid=I123C-as
However, a visit from LinkedIn looks like this:
RAW: None
PHP: None
REFERRER IP: 89.127.12.32
USER AGENT: Mozilla/5.0 (Windows NT 10.0; Win64; x64)
AppleWebKit/537.36 (KHTML, like Gecko) Chrome/71.0.3578.98 Safari/537.36
REFERRAL TYPE: external
URI: /how-speed-affects-your-website/
Any ideas why there is no referer data being transferred from LinkedIn? or any thoughts on how I can observe visits from LinkedIn by any other means?

Answer 1

Is your own site using HTTPS? And do those links the users follow use HTTPS URLs?
If not, you will simply not get a referrer from LinkedIn in modern browsers, due to Referrer-Policy.
no-referrer-when-downgrade (default)
This is the user agent's default behavior if no policy is specified. The URL is sent as a referrer when the protocol security level stays the same (HTTP→HTTP, HTTPS→HTTPS), but isn't sent to a less secure destination (HTTPS→HTTP).
https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Referrer-Policy#Directives:
LinkedIn doesn’t actively specify a Referrer-Policy as far as I can see, so this fallback value will be used automatically.
So if your site doesn’t support HTTPS, or the links go to the HTTP version first, the browser is forbidden from sending you this info.
or any thoughts on how I can observe visits from LinkedIn by any other means?
Check if they append any specific, uniquely named tracking parameters to outgoing links, like Facebook does with the ?fbclid=I123C-as. Then you could take the existence of that parameter as an indicator that the user most likely followed a link from LinkedIn to your site.