Add login to Newgrounds extractor

[mrmedieval]

IMPORTANT: PRs without the template will be CLOSED

Description of your pull request and other information

Add a login function to Newgrounds extractor to fix issues with adult media.

Fixes #9324

Template

Before submitting a pull request make sure you have:

• [ x] At least skimmed through contributing guidelines including yt-dlp coding conventions
• [x ] Searched the bugtracker for similar pull requests
• [x ] Checked the code with flake8 and ran relevant tests

In order to be accepted and merged into yt-dlp each piece of code must be in public domain or released under Unlicense. Check all of the following options that apply:

• [x ] I am the original author of this code and I am willing to release it under Unlicense
• I am not the original author of this code but it is in public domain or released under Unlicense (provide reliable evidence)

What is the purpose of your pull request?

• [x ] Fix or improvement to an extractor (Make sure to add/update tests)
• New extractor (Piracy websites will not be accepted)
• Core bug fix/improvement
• New feature (It is strongly recommended to open an issue first)

[bashonly]

Thanks for the PR. Before reviewing, I have some questions:

• Does passing cookies currently work with the extractor? I tried asking here and got no response: [Newgrounds] Error 401, Adult-rated video NSFW #9324 (comment)

• Why remove the code that extracts the media from the webpage? Is it to fix/prevent [newgrounds] Cookies causes video to download profile page #6488 ?

• Does extracting media from the webpage still work without cookies?

• What kind of response do you get from the site when login fails to due invalid username/password?

[mrmedieval]

1. Passing cookies works on my pull request, but not on the current version, because of [newgrounds] Cookies causes video to download profile page #6488
2. Removing media extractor fixes [newgrounds] Cookies causes video to download profile page #6488. I believe this issue has to do with the media extractor's regex. Videos still download with the code removed.
3. Without cookies, or with an invalid login, the download will fail with "Unable to download webpage: HTTP Error 401: Unauthorized".

[Grub4K]

While trying to test this extractor I found that some of the old tests are no longer up to date, and went down deeper and deeper the rabbithole. I went on to fix the tests first, which shows us that the removed code is required to download audio and flash content.

The reason why the download with login was failing is that the "url":\s*"[^"]+" matches the json for the user info. Specifying a more locked down embedController\(\[{ before manages to only capture the audio. After a lot of experimentation I found that this is easier than to parse the whole thing as JSON since that contains callback code and inline function invocations.

3. Without cookies, or with an invalid login, the download will fail with "Unable to download webpage: HTTP Error 401: Unauthorized".

I think the question was more about what response you get when failing to log in. I eventually managed to get a JSON response by passing the X-Requested-With headers as gets done by the media api call.

See master...Grub4K:yt-dlp:fix/newgrounds for what I eventually ended up with

[mrmedieval]

See master...Grub4K:yt-dlp:fix/newgrounds for what I eventually ended up with

I am very impressed with that solution. I'm still a novice, so it took a lot of trial and error to find out what I did about the extractor. I'm very happy to see the issues with the extractor fixed, and I hope some of what I did was helpful.