I am creating a secure web based API that uses HTTPS; however, if I allow the users to configure it (include sending password) using a query string will this also be secure
I don't agree with the statement about [...] HTTP referrer leakage (an external image in the target page might leak the password) in Slough's response.
The HTTP 1.1 RFC explicitly states:
Clients SHOULD NOT include a Referer header field in a (non-secure) HTTP request if the referring page was transferred with a secure protocol.
Anyway, server logs and browser history are more than sufficient reasons not to put sensitive data in the query string.