Function do_bearer_auth 

pub async fn do_bearer_auth<T: BearerAuthBackendApi + ?Sized>(
    api: &T,
    now: SystemTime,
    user_key_pair: &KeyPair,
    lifetime_secs: u32,
    scope: Option<Scope>,
) -> Result<TokenWithExpiration, BackendApiError>

Create a new short-lived BearerAuthRequest, sign it, and send the request. Returns the TokenWithExpiration if the auth request succeeds.