Best way to track where visitors come from? - google-analytics-api

Question

I am running an advertisement network where the publishers can post affiliate links in their blogposts that they then can earn money on with pay-per-click.
It is very important for us to make sure that the clicks are as natural as possible and we are automatically checking many parameters to make sure it is. One of the way we check this is to look if the visitor (The person who click the affiliate link) is coming from the bloggers website or not. This is to make sure that the publisher does not post his link on other services but his blog.
To do this we use HTTP_REFERRER in PHP, but as you all know it's not 100% reliable. About 50% of our visitors have this disabled. This means that we still catch cheaters if they get multiple clicks from a false source, if they for example get 10 clicks from 10 unique visitors, then usually atleast one of these have a referrer and we can see that the publisher is cheating.
I'm writing here to see if there are any other solutions to this than the HTTP_REFERRER? For example:
Can we use Google Analytics API to check this data instead?
If 9 visitors have HTTP_REFERRER disabled, but we get the data from the 10th one, can we match that data together with the other 9 somehow? For example maybe there is some other information but the HTTP_REFERRER included in each visit, that would match if they came from the same referrer.
Any other ideas?

Answer 1

In PHP you can access a $_SERVER variable that is called HTTP_REFERER.
$_SERVER["HTTP_REFERER"]
To understand what this variable is, you really gotta look at HTTP.
When a browser loads up a website it sends a request to the web server hosting the website that looks something like this:
GET / HTTP/1.1
Host: example .com
Connection: keep-alive
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/48.0.2564.116 Safari/537.36
The web server will then send the page that was requested back to the browser.
Now imagine that you were on a webpage, and clicked on a link that takes you to another page (example: Google), the browser will then send a similar request to the one above, but it will look like this:
GET / HTTP/1.1
Host: google .com
Connection: keep-alive
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/48.0.2564.116 Safari/537.36
Referer: http://example .com
If you see that there is an extra line called Referer, this tells the website you are visiting where you came from when you clicked a link to the site.
This is often used for analytic purposes, if you have a blog and you shared a post that you published, you would want to know where people are coming from so that you know which place will give you the most traffic in the future, etc.
In PHP, this is the value that is put in the variable
$_SERVER["HTTP_REFERER"] // http://example .com

Answer 2

You can use the Google Analytics API to check for this, with the caveat that if javascript is not enabled OR if the user has taken steps to block tracking by Google Analytics, their data will not show up.
Use the fullReferrer dimension to get the source and referral path (i.e. website name and URL where you can find the link to your site).
You can also use Google Webmaster Tools to see who is linking to your site. Look under Search Traffic > Links to Your Site and you will see the full list. This may help you to find those sites where your publishers have posted their affiliate links.