I'm trying to setup openId Connect custom auth provider. WHen selecting apex class for registration handler, I would like to see which user data apex class gets from my IDP userInfo. When I set debug logs to apex class and try to use some of the test URLs, there is no log in debug logs. 

Also, since this apex class is part of whole authentication process with redirect calls in between IDP and salesforce it is not possible to debug with developer console. 

Any idea how to catch this kind of logs?