/backport to stable28

At least on Debian, the MIME type is added automatically for all webservers, with their own configs or /etc/mime.types, so this part is probably less important. However, in which case and which absolute directory are you expecting conf/mime.types? Like this, me, and hence I guess many others, won't be able to know what to do, if the correct MIME type is really not served anyway. Not sure whether /etc/mime.types is used across all (relevant) distros and webservers, but this is probably a more clear config to look at? For Apache otherwise /etc/apache2/mods-available/mime.conf, or of course any other server/vhost config.

Just checked back: Nginx uses /etc/nginx/mime.types, Apache and Lighttpd use /etc/mime.types.

What I was actually missing in the docs was not the MIME type (still good to mention it), but the rewrites: The default/example webserver configs rewrite everything to index.php, which is not explicitly excluded from the rewrite, via RewriteCond in Apache, and location ~ \.(?:...|mjs|...) { block in Nginx.

Another thing is the Cache-Control header. So basically 3 things:

1. Assure that requests to .mjs are not rewritten to index.php but served directly.
2. Assure that .mjs files are served with text/javascript MIME type.
3. Serve .mjs files with Cache-Control "max-age=15778463" header, like other static assets, respectively Cache-Control "max-age=15778463, immutable" for those with v= query parameter.

All of this can be usually achieved by adding mjs to the list(s) of asset file extensions in the existing Nextcloud webserver config.

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