This is a very barebones implementation of a CORS proxy that also attempts to pass the correct referrer information to bypass server-side restrictions to hotlinking.
To use this, simply append an image's direct URL to the end of https://img-referrer-tunnel.herokuapp.com/, so for example, https://img-referrer-tunnel.herokuapp.com/https://i.imgur.com/RbnS7Ba.jpeg.
If the origin server is rejecting the response, try playing with the host query parameter. For example, https://img-referrer-tunnel.herokuapp.com/https://i.imgur.com/RbnS7Ba.jpeg?host=imgur.com.
In order to skip the host parameter requirement, known domains are mapped to the host the server expects. Currently known mappings are stored in mapping.json.
Every URL in endpoints.json will be tested against the proxy to verify that the proxy successfully loads.
If you'd like to add an additional mapping, feel free to open a PR. Please also add a test for the domain if you do so.