rest api httpauth if only ldap authentication is enabled

With the following setup:

- guest access disabled
- authentication: ldap only

How do I access the rest api (not from the build script where I can use the generated user name and password stored in teamcity.auth.userId and teamcity.auth.password) from custom code?

If I login using my browser, no problem, I can access get requests from the browser (like /app/rest/version).
If I logout and paste the rest request into the browser, the basic auth form pops up but it does not accepts my user name and password (what I can use for regular login)

What am I missing?