Etherpad Widget doesn't check if the pad name is allowed

[Nostradamos]

Seems like https://scalar.vector.im is quite strict with the allowed pad names. But it's possible to enter an illegal pad name and embed the pad, which then results in a iframe which cannot get displayed correctly, because the pad url only reports Such a padname is forbidden.

[florianjacob]

I experience similar behaviour when when I use etherpad names that are too long: ABCDEFGHIJKLMNOPQRS as pad name, i.e. 20 chars long works just fine, but ABCDEFGHIJKLMNOPQRST, i.e. 21 chars long, break. I do get a 502 bad gateway and the not embeddable banana like in element-hq/element-web#9098, though, not such a padname is forbidden.

[jaywink]

Thanks @florianjacob I opened a new issue since this is separate related to purely the Etherpad widget and name length of the pad: https://github.com/vector-im/riot-web/issues/10485