You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: client.rs
    path of file: ./repos/tonic/examples/src/authentication
    
    the code of the file until where you have to start completion: pub mod pb {
    tonic::include_proto!("grpc.examples.unaryecho");
}

use pb::{echo_client::EchoClient, EchoRequest};
use tonic::{metadata::MetadataValue, transport::Channel, Request};

#[tokio::main]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
    let channel = Channel::from_static
    
async fn main() -> Result<(), Box<dyn std::error::Error>> {
    let channel = Channel::from_static("http://[::1]:50051").connect().await?;

    let token: MetadataValue<_> = "Bearer some-auth-token".parse()?;

    let mut client = EchoClient::with_interceptor(channel, move |mut req: Request<()>| {
        req.metadata_mut().insert("authorization", token.clone());
        Ok(req)
    });

    let request = tonic::Request::new(EchoRequest {
        message: "hello".into(),
    });

    let response = client.unary_echo(request).await?;

    println!("RESPONSE={:?}", response);

    Ok(())
}