OWASP is an excellent resource and you could spend days reading it and months implementing all of its suggestions ... as some companies do. However, there are thousands of web sites (made using frameworks and otherwise) that are pure-and-simple sloppy. Plainly revealing that they were constructed in haste and that the developers only tested the “intended” routes before declaring the project “Done.” It was anything but.
The HTTP protocol, because it is stateless, is actually difficult to properly test. Nevertheless, stress-testing and smoke-testing and crap-testing tools do exist. The question before the house is whether they have actually, ever, been used to any serious degree. Interestingly, when we beat a site up and then turn in a report of some of the failures that we found, the developers often get a curious look on their face and said, “yeah, we saw that happen once ...” (We could make it happen at will.)