Because the sessions module of this crate is already able to verify access tokens,
it was not much more work to turn this into a Rocket 0.4+ Guard.
The implemented Guard (enabled by the feature "rocket_support") allows access to http paths if the provided http "Authorization" header contains a valid "Bearer" token. The above mentioned validations on the token are performed.
See the rust documentation for firestore_db_and_auth::rocket::FirestoreAuthSessionGuard.