fix: emit allow attribute on iframe for the clipboard (fixes #3474)

[vmiklos]

As described at
https://sites.google.com/a/chromium.org/dev/Home/chromium-security/deprecating-permissions-in-cross-origin-iframes newer Chrome requires explicit markup for code in an iframe to execute JS that requires permissions, like clipboard.

If this markup is missing, then the user won't be even asked. Use the wildcard syntax, because the COOL JS code in the iframe is not the initial src attribute value of the iframe, it gets changed later.

With this, a permission popup on paste shows up in Chrome even if the paste is perssed on the notebookbar, even if nextcloud is served from one domain and COOL is served from an other domain.

This fixes the document edit case; possibly it should be also added at all other places where the allowfullscreen attribute is used, which is not done in this commit.

• Resolves: iframe lacks allow attribute to use navigator.clipboard in Chrome #3474

[vmiklos]

To clarify, this patch fixes the main, editing use-case. There are other places where allowfullscreen is used, and possibly this new allow attribute should be added there as well. One place is the read-only view of past revisions. I think we currently don't support copy for read-only views, so it's not useful to have this attribute there (although it doesn't hurt, either).

[vmiklos]

@juliushaertl could you please review this? Thanks.

[juliusknorr]

To clarify, this patch fixes the main, editing use-case. There are other places where allowfullscreen is used, and possibly this new allow attribute should be added there as well. One place is the read-only view of past revisions. I think we currently don't support copy for read-only views, so it's not useful to have this attribute there (although it doesn't hurt, either).

Yes, would be good to just apply that consistently to any iframe:

files.js
98:		const $iframe = $('<iframe data-cy="documentframe" id="richdocumentsframe" nonce="' + btoa(OC.requestToken) + '" scrolling="no" allowfullscreen src="' + documentUrl + '" />')

document.js
208:			// iframe that contains the Collabora Online Viewer
209:			const frame = '<iframe data-cy="coolframe" id="loleafletframe" name="loleafletframe_viewer" allowfullscreen nonce="' + btoa(getRequestToken()) + '" style="width:100%;height:100%;position:absolute;"/>'
268:			// iframe that contains the Collabora Online
269:			const frame = '<iframe data-cy="coolframe" id="loleafletframe" name="loleafletframe" nonce="' + btoa(getRequestToken()) + '" scrolling="no" allowfullscreen style="width:100%;height:100%;position:absolute;" />'

[vmiklos]

Yes, would be good to just apply that consistently to any iframe:

Will do that in a next PR.

[juliusknorr]

/backport to stable28

[juliusknorr]

/backport to stable27

[juliusknorr]

/backport to stable26

[backportbot]

The backport to stable26 failed. Please do this backport manually.

# Switch to the target branch and update it
git checkout stable26
git pull origin stable26

# Create the new backport branch
git checkout -b backport/3475/stable26

# Cherry pick the change from the commit sha1 of the change against the default branch
# This might cause conflicts, resolve them
git cherry-pick 2e9441c5

# Push the cherry pick commit to the remote repository and open a pull request
git push origin backport/3475/stable26

Error: No changes found in backport branch

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