pub mod pb {
    tonic::include_proto!("grpc.examples.unaryecho");
}

use pb::{EchoRequest, EchoResponse};
use tonic::{metadata::MetadataValue, transport::Server, Request, Response, Status};

type EchoResult<T> = Result<Response<T>, Status>;

#[derive(Default)]
pub struct EchoServer {}

#[tonic::async_trait]
impl pb::echo_server::Echo for EchoServer {
    async fn unary_echo(&self, request: Request<EchoRequest>) -> EchoResult<EchoResponse> {
        let message = request.into_inner().message;
        Ok(Response::new(EchoResponse { message }))
    }
}

#[tokio::main]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
    let addr = "[::1]:50051".parse().unwrap();
    let server = EchoServer::default();

    let svc = pb::echo_server::EchoServer::with_interceptor(server, check_auth);

    Server::builder().add_service(svc).serve(addr).await?;

    Ok(())
}

fn check_auth(req: Request<()>) -> Result<Request<()>, Status> {
    let token: MetadataValue<_> = "Bearer some-secret-token".parse().unwrap();

    match req.metadata().get("authorization") {
        Some(t) if token == t => Ok(req),
        _ => Err(Status::unauthenticated("No valid auth token")),
    }
}