Add OAuth2 support

The purpose here is to add a new JAAS LoginModule allowing authentication based on JWT.

We can use Nimbus JWT dependency to deal with that.

The idea is:
1. Introduce a new `OAuth2LoginModule` to be used by the `JaasAuthenticationPlugin`, similar to the existing `PropertiesLoginModule` or `LDAPLoginModule`.
2. Validates tokens locally, to avoid systematic call to the IdP on every connection.
3. The OAuth2 configuration (issuer, claim, etc) is defined in the `conf/login.config` as other `LoginModules`.
4. The user pass the token as "password"