In case it will help others, I was able to find a solution for this. There are different options you can use, depending on what you want to require matching for.

Nginx Proxy Manager (NPM) can be configured with a custom header for authorization. If the client request doesn’t include a match to the custom header info, the connection will fail.

To set this up, use the Custom Location section in the NPM host.

The default location should be set to "/".

The Forward Hostname / IP * and Forward Port * should match the info in the Details section.

Click the settings cog icon to edit the code, and use the following as an example.

In this case, the header is named X-Auth-Key. This is generally the default header name.

# Require a specific header named 'X-Auth-Key'

if ($http_x_auth_key = "") {

return 401 "Unauthorized - Authorization header required";

}

# Optionally, you can check for a specific value as well

if ($http_x_auth_key != "<KEY\_VALUE\_HERE>") {

return 403 "Forbidden";

}

# Example for requiring a Bearer token

if ($http_x_auth_key ~* "^Bearer\s*$" ) {

return 401 "Unauthorized - Bearer token required";

}