Method discoverResourceUrl does not check response type

Problem/Motivation

UrlResolver::discoverResourceUrl is called as part of the public method getProviderByUrl. The method makes an HTTP GET request to the provided URL, and tries to parse the response body as HTML. But nowhere does it check the type of response, via the Content-Type header. That means it can try to erroneously parse non-HTML contents as HTML.

Steps to reproduce

Call UrlResolver::getProviderByUrl with a URL that does not return HTML.

Proposed resolution

Check the Content-Type headers before parsing as HTML.

Remaining tasks

User interface changes

n/a

Introduced terminology

API changes

n/a

Data model changes

n/a

Release notes snippet