Add config option to manually define Rack url scheme

[tarragon]

We need to run Puma behind a service that is unfortunately not passing down HTTP_X_FORWARDED headers. We also need to run Puma on a port other than port 443 and not in SSL mode, while the frontend service handles the SSL.

This has caused a problem within Puma where redirects generated by Rails (notably on session create) use http rather than https and this is confusing clients and the frontend service.

The only way I can find in Puma itself to set Rack's url scheme is with this line in lib/puma/request.rb:

env[RACK_URL_SCHEME] = default_server_port(env) == PORT_443 ? HTTPS : HTTP

Following the thread, default_server_port checks if Puma is running in SSL mode, then checks if the X_FORWARDED headers are there, returning PORT_443 in this case, otherwise PORT_80. To work around this I have monkey patched default_server_port to return PORT_443 in our environment regardless.

It would be great to be able to more explicitly control the Rack url scheme, and I suggest that the port assumptions here could do with refactoring for environments where Puma is running on a custom port (neither 443 or 80).

If there's some other way to achieve what I'm trying to achieve or if I've missed some configuration option, please let me know.

[MSP-Greg]

Makes sense, as the frontend really defines this. I think adding a config option, and, if it's not set, the current setting (as shown above) will be used. I'll post a PR soon...

[tarragon]

Hey there, I notice this has a contrib-wanted label now, is there anything I can do to help?

[MSP-Greg]

I'm adjusting some things in PR #2586, which adds the feature... Thanks.