REST API, custom fields and permissions question

Hello,

I'm writing a custom interface to the YouTrack system using the REST API.
Everything seems to work fine but I'm noticing some inconsistencies regarding permisions and certain parts of the api.

For instance, I have a user with the (predefined) developer role. This user can login and edit custom fields (like priority), so that user has access to the list of custom fields in that project (priority, state, ...).

However, using the REST API I can't seem to find any way to retrieve that list (all possible custom fields for an issue).

/rest/issue/<issueId>
this only returns the field where a value has been set for, and it doesn't show me which bundle is being used for an already filled value.

the method "/rest/project/all" also doesn't give me the custom fields

this method however: "/rest/admin/project/<project>/customfield" gives me exactly what I need, BUT for this call the user would need "Read Project" permission (which I don't think can ask of the user).

Is there any workaround to get the list of fields for an issue without extra permissions needed (a developper role should suffice), or am I doing something wrong?

Thanks for reading! :)