Fix naming, match constructor args to fields

I'm using spring-data to persist the OAuth2Authentication in a MongoDB. When reading the OAuth2Authentication from MongoDB this excpetion is thrown.
```
org.springframework.data.mapping.model.MappingException: No property clientAuthentication found on entity class org.springframework.security.oauth2.provider.OAuth2Authentication to bind constructor parameter to!
```
( I know it's kind of risky to rely on the automatic mapping for classes that you do not own :smirk: )