How to access /admin urls with read-api?

[TLINDEN]

I installed the write-api plugin, created a master token and I am able to access the usual suspects such as /api/users or /api/topics via the read-api.

However, I cannot access backend url's:

% curl -H "Authorization: Bearer $token" "https://www.foo.bar/api/admin/manage/privileges/?_uid=1"
"not-authorized"

If I access this url via chrome (once logged in into the admin backend), I get JSON output as expected.

Is this unsupported or am I doing something wrong?

best,
Tom