Improve OAuth2 Resource Server tests

[henriquels25]

Summary

The tests for the OAuth2 Resource Server sample only include GET requests.

I believe it would be useful to add examples for other HTTP methods (POST, PUT, PATCH, DELETE) because the code for testing them is different.

Sample

In this project it's possible to see that if the same technique used for testing the GET requests is used for a POST, the test fails without sending the CSRF token in the request.

In this example, I created a working POST request test example based on the sample, based on the explanation contained on this StackOverflow question.

[jzheaux]

@henriquels25 I agree that additional tests would be helpful; would you be interested in submitting a PR?

[henriquels25]

@jzheaux I submitted a PR with examples for a POST request. I didn't create examples for the other HTTP methods to keep the sample small, as the code for testing them is not different.