added an RFC 7662 compliant OAuth2 auth adapter (#4910)

* 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

src/Adapters/Auth/AuthAdapter.js

@@ -3,9 +3,10 @@ export class AuthAdapter {
   /*
   @param appIds: the specified app ids in the configuration
   @param authData: the client provided authData
+  @param options: additional options
   @returns a promise that resolves if the applicationId is valid
    */
-  validateAppId(appIds, authData) {
+  validateAppId(appIds, authData, options) {
     return Promise.resolve({});
   }