This commit updates the whitelist we're using for outgoing links from HedgeDoc. Previously, any URI scheme except javascript: could be used as long as it contains two slashes after the scheme (like https://). On the one hand this allowed linking to arbitrary and possibly unsafe URI schemes, on the other hand this breaks some schemes like xmpp: or geo:.
We're now using the list of schemes that can be registered by a browser to be opened. This restricts arbitrary scheme usage but on the other side fixes several other schemes.
Signed-off-by: Erik Michelson <github@erik.michelson.eu>
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