A seperate header is used instead of relying only on current cookie
because the current cookie is difficult to modify before being
forwarded, and would make removing invalid cookies in responses
complicated.
Includes the associated Go functions for inserting and selecting given a
specific user ID or subscription ID. Also adds required HTML tags and
HTTP queries for subscription process during user registration.
To make requests to Go API endpoints for registration from a PHP page,
there needs to be local routing between the two servers. This method
avoids needing Apache installed seperately for development builds while
allowing it to still be used in production if necessary.