How to Integrate a Third-Party API with CMS Made Simple?

[Jo Morg]

I'm assuming that you are talking about PHP 3rd-party APIs.
There are a few ways to do that, one being exactly by using an UDT. It's not a bad solution for smallish integrations since the code is evaluated and that has some impact on site speed. Now I've been researching a bit for the last few years and the speed impact of evaluated code is lesser and lesser with each new PHP version and UDTs are so versatile that I'm using them more and more for quick interventions on clients' sites.
Sometimes the use of evaluated code is considered a bad practice, in part because of the possibility of public access to code injection if eval is used on frontend user inputs, but that is also a valid concern with any PHP script so make sure you sanitize user input if used.
Another possibility, if you are a PHP coder, is by creating a simple Smarty plugin and put it on the assets/plugins folder of the site. pretty much what can be done with UDTs can be done with a Smarty plugin, it's just the wrapper that is a little different and, as is the case with UDTs you can call them directly from a Smarty template. In this case the code is included, not evaluated.
If you are somewhat familiarized with the CMSMS Module API, creating a simple module is actually simple, you can then create your own PHP classes and if you put them in the lib folder of your custom module CMSMS will include them automatically as long as you prefix the file names with class., like so: class.<classname>.php. One or several of the classes can be wrappers for the 3rd-party API or just include it and setup it up to be used anywhere in CMSMS. This is the most versatile way and IMO the best one.
How you do it depends a bit on the scope of the project and how comfortable you are with coding.

HTH