amp-youtube: "No cookie" option

[saitho]

What's the issue?

In some cases it might be necessary to embed a YouTube video without cookies (legal reasons et cetera). There is a way to embed the YouTube player without cookies with a special embed URL – you just have to add "-nocookie" between youtube and .com.
E.g. https://www.youtube-nocookie.com/embed/jpyHTTtddUo?enablejsapi=1

Implementation proposal

• Add a new property "credentials" similarly to https://www.ampproject.org/docs/reference/components/amp-list#credentials-(optional)
• Add a new private method "getEmbedUrl()" that when this new property...
  • is not set: returns the URL that currently used (default)
  • is set: return the nocookie-url: https://www.youtube-nocookie.com/embed/${encodeURIComponent(this.videoid_ || '')}?enablejsapi=1
• use "getEmbedUrl()" in method getVideoIframeSrc_() (line 156 of current code)
• add property to documentation and update validation rules

What browsers are affected?

None, as this is a new feature.

Which AMP version is affected?

None, as this is a new feature.

[aghassemi]

@saitho Thanks, good feature to add. Would you be interested in contributing this feature by sending a PR? AMP is fairly streamlined for quick external contributions. If you are interested, checkout https://github.com/ampproject/amphtml/blob/master/CONTRIBUTING.md to get started.

[saitho]

I already thought about that. :) I'll be discussing that with my company.

[aghassemi]

@sahirsait for the attribute, let's use credentials with values of omit and include instead of nocookie.(with default of include). This will align better with amp-list which already has such a mode.

[saitho]

That makes sense. I changed the attribute name in the issue text.