* added an RFC 7662 compliant OAuth2 auth adapter
* forgot to add the actual auth adapter to the previous commit
* fixed lint errors
* * added test coverage
* changed option names in auth adapter from snake case to camel case
* added underscore prefix to helper function names
* merged consecutive logger calls into one call and use JSON.stringify() to convert JSON objects to strings
* changed error handling (ParseErrors are no longer thrown, but returned)
* added description of the "debug" option and added this option to the tests too
* added a check of the "debug" option to the unittests and replaced require() of the logger with an import (the former does not work correctly)
* added AuthAdapter based auth adapter runtime validation to src/Adapters/Auth/index.js, added capability to define arbitrary providernames with an "adapter" property in auth config, replaced various "var" keywords with "const" in oauth2.js
* incorporated changes requested by flovilmart (mainly that oauth2 is now not a standalone adapter, but can be selected by setting the "oauth2" property to true in auth config
* modified oauth2 adapter as requested by flovilmart
* bugfix: defaultAdapter can be null in loadAuthAdapter() of index.js (my change broke the tests)
* added TODO on need for a validateAdapter() to validate auth adapters
* test cases and cleanup
019cf0a986