Fluid Topics proposes a way to authenticate on-the-fly by entering user credentials when sending a request. It is based on Basic Access Authentication.
The following header can be used to authenticate as Aladdin / open sesame.
Authorization: Basic QWxhZGRpbjpvcGVuIHNlc2FtZQ==
Both the user's email address and password must be encoded, as in the following example using the command line:
echo -n '<email@example.com>:<password>' | base64