You're requiring PHP 8.3 but not using some of the most powerful tools in 7+: strict types.
```
/* @var array<string, mixed> Variables stored in the context */
private $variables = [];
```
This should be typed as `array` (heck, I'd argue ArrayObject instead) and all your classes should have `declare(strict_types=1);` at the top.
Your `Dumbo\Helpers` classes are basically static mine traps that you are unable to mock in unit tests. Why does `BasicAuth` expose a single static method but then calls a bunch of other static methods? What ends up happening in any class that uses any of your `Dumbo\Helpers` classes will always run whatever code is defined in these helper classes.
I'm unsure where the bootstrapping process begins. What file does your webserver need to call to handle a new request? I am hoping it is within a root-level directory and not at the root level itself. In other words, `/public/index.php` vs `/index.php`. Your quickstart in README.MD makes it pretty clear that you expect the latter, which is highly unsafe. See any number of poorly configured webservers that stop processing PHP for any reason but now show your site's full contents to anyone passing by.
I would strongly argue against _any_ magic in your framework. Specifically, routes: they should be explicitly defined. I still work with a legacy Symfony 1 framework project and I can't tell you how much I detest magic routing. For a modern example see how Symfony 2+ requires explicit route definition. Heck, how it requires explicit everything because magic should be left to magicians.
Your framework seems like it can only handle `application/json` and `application/x-www-form-urlencoded` requests, but not `multipart/form-data`.
Take these as positive criticisms of your work. It's "fine". I wouldn't use it, I would actively recommend against using it, but I would actively recommend against using anything that's not Symfony (or Laravel if I were drunk). I do not think your project is at the "Show HN" level - it is still far too under-developed.