• I've read the guidelines for Contributing to YOURLS Projects
• This request isn't a duplicate of an existing issue
• I've read the docs and followed them (if applicable)
• This is not a personal support request that should be posted on the YOURLS Discourse community

Describe the bug
yours_get_request uses HTTP_HOST to divine the full URL of the shortlink request but, if yourls is running in a Docker container and it is being proxied from a non-root path, that logic is faulty.

To Reproduce
Steps to reproduce the behavior:

1. Set up a yourls Docker container with YOURLS_SITE set to the "external" FQDN URL including the "/app" path (see step 2).
2. Configure Apache to proxy "/app" to the underlying YOURLS instance.
3. Try to retrieve a short link.

Expected behavior
The underlying full link associated with the short link is returned.

Actual behavior
YOURLS fails to return the link because the use of the Apache variables causes the path to be left in the request field, thereby failing to match the shortlink.

Versions
1.7.6 in a Docker container.