mod_http_oauth2: Add service documentation URL to metadata This is aimed to those building integrations, so the modules site seems appropriate. Configurable so that a deployment can point to their own OAuth documentation.

This module lets you block connections to any remote servers not on a
whitelist.

``` {.lua}
modules_enabled = {
    -- other modules --
    "s2s_whitelist",

}
s2s_whitelist = {
    "example.org",
}
```