Debug LTI 2 ToolProxy registration

by Pablo Platt.  

Hi,

I'm implementing a tool provider.
When sending the tool proxy to /mod/lti/services.php/toolproxy I'm getting back 400 Bad Request response.
I'm not sure if the error is because of a bad oauth signature or bad ToolProxy message format.

How can I debug what's wrong with my request?
I tried setting the Debug Messages to Developer in admin/settings.php?section=debugging and I checked /var/log/nginx/error.log but I don't see errors.
Is there other way to enable logging or do I need to look somewhere else for the log files?

Thanks