Integrates Facebook as an external OAuth2 provider.
The unique identifier and th expected value in the X-OAuth2-Provider header is Facebook.
The following configuration properties are supported:
oauth2.authorization.proxy.server.springboot.providers.facebook.appId: the application id of the Facebook application.oauth2.authorization.proxy.server.springboot.providers.facebook.appSecret: the application secret, currently optional.
The Facebook OAuth2 provider is only used if the oauth2.authorization.proxy.server.springboot.providers.facebook.appId
is provided by the application, otherwise none of the beans are created, and thus the Facebook OAuth2 provider won't be
available.
Facebook4J is used for the integration.
The Facebook class's getOAuthAccessTokenInfo and
getMe methods are used to verify the given access token and retrieve the user information from Facebook.
The Facebook Graph API Explorer can be used for testing access tokens provided by Facebook.