Allow OAuth2Authorization to be extensible

[Chr3is]

Expected Behavior
The OAuth2Authorization is extendable and a custom instance can be created.

Current Behavior
It is possible to extend the OAuth2Authorization but not to instantiate the fields within the parent OAuth2Authorization.

Context
see #1203 (comment)

[Chr3is]

@jgrandja can you assign this issue to @c3mig?

[jgrandja]

@Chr3is Can you have @c3mig respond to this issue? I can't see the name in the assignees pick list. It will show up after they respond here.

[c3mig]

@jgrandja Should be assignable now - thanks.

[Balaji-Murugaiya]

@jgrandja @Chr3is Can I take this up?

[jgrandja]

@Balaji-Murugaiya Thanks for the offer but this is currently assigned to @c3mig.

Although there hasn't been anything submitted as of yet, this enhancement does not appear to be needed since there are no upvotes. We will likely hold off on this for now.