When I try to call:
https://sonar.mydomain.com/api/resources?resource=com.mydomain.project:MY&metrics=ncloc&format=json
I get
{"err_code":401,"err_msg":"Unauthorized"}
How do I pass my credentials?
According to the documentation SonarQube uses basic authentication. Try:
curl -u admin:SuPeRsEcReT "https://sonar.mydomain.com/api/resources?resource=com.mydomain.project:MY&metrics=ncloc&format=json"
Obviously the mechanism for passing these credentials is dependent on how you are invoking the API.
This should also work from the web browser. Try logging into the Webui, your browser will normally cache the credentials.