@matthew_buckett - The issue is resolved. A big thanks to you for spending time in resolving my issues.

In my canvas instance, dynami_settings.yml file was missing. So, I did a copy of .example file using command cp dyanmic_settings.yml.example dynamic_settings.yml. Also, I edited the dynamic_settings.yml file by changing 'development' section to 'production' section. Then, I did a restart to my canvas instance using command opt/bitnami ctlscript.sh restart. 

On clearing browser cache, login_required error was resolved and I got the id_token from canvas in my redirect_uri.

Thank you very much for guiding me through my issues.