A web service w/ server processing job creating Adobe files from Adobe Script?

Getting a special license for Ai-server capabilities has to be a very costly endeavor whereby not only does one have to pony-up the budget but also be able to contact the appropriate Adobe personnel in the first place. Calling the regular sales phone-line won't do, (unless things have changed) as the sales-people will have no idea what you're talking about. Furthermore, to truly be able to use an Illustrator on a server would require extensive C++ SDK development for best results. The reason being, it was never built with UI-less performance in mind as the foundation, as is the case with InDesign. Therefore, processing time and run-time errors, especially errors cause due to rendering will create a non-scalable scenario if one were to simply stick an Illustrator on a server and start feeding it all sorts of arbitrary API calls with the expectation of immediate and convenient results. There are decades-old MRAP errors when scripting is used, and they can be unpredictable and irreproducible - seemingly appearing at random during certain operations. Hence the necessity to do the heavy C++ development for any such thing, in my personal opinion. (Thoughts?)
However, if you were to simply use this setup in-house at some company where a multitude of users are already licensed with their own desktop CC license, Adobe staff have mentioned before on these forums (back when they were more searchable and accessible) that it would in fact be allowed and legal provided that only licensed users could access this API. (No secretary getting Ai-generated documents magically in the front office, unless they are also licensed with own desktop CC license)
If this is your case, or if this kind of environment would foster experimentation on your part to then further explore the possibilities as a mockup of sorts, then you can probably make it happen real easy (relatively speaking). All you would really need is for example, a running computer accessible via the intranet WiFi at your organization, a PHP page to receive web calls and then trigger a JSX script. This could be an exciting and fun exercise if you have time for it, because there is certainly something magical about being able to remotely activate a desktop application and get a downloaded document back on an entirely different computer. However this same exercise would be a good benchmark for the features in which the application or scripting would fall short on as far as performance goes. For example, say about 1/20 of your operations incur a MRAP error which then re-occurs every time after it appears. Now you need a procedure to restart Illustrator and try again. But how far along the process did you get before it quit? Maybe it was a several-document operation and it did about 5 out of 10 documents, each one taking a long time. So now you have to do this and that to keep track of various things. Then, while all this is going on, there's 5 other of your workers sending their API calls and clicking over and over because it's not responding at all. So now, maybe you have to have a queue or virtual machines to hold multiple application instances, it can get to be a mess!

Contrast this with InDesign server whose yearly cost is (relatively speaking, again) in the teens of thousands of dollars, which is a small price to pay considering you can be processing legally-web-inputted data while you sleep, 365 days per year - and ID is built to run without any UI from the ground-up. Illustrator absolutely has to have UI in order to work and has no concept of background tasks.

Anyways, that's my knowledge from years of hanging out here and barking up that tree.

Adobe not allowed Illustrator works as a server process.
In your case, The use of InDesign Server is the only way.

You say you want your webservice to generate an Illustrator file or PDF with some paths. PDF is an open format and you can generate a simple PDF file from scratch using a scripting language like php.

Check the license, or have your legal team check it. The standard license is for one person only. A web app may be used by many people. Generally you need a server license, and this has sometimes cost companies millions if they used a single license, and were charged for each web visitor.