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: challenge.rs
    path of file: ./repos/azuredatastudio/cli/src/tunnels
    
    the code of the file until where you have to start completion: /*---------------------------------------------------------------------------------------------
 *  Copyright (c) Microsoft Corporation. All
    
pub fn sign_challenge(challenge: &str) -> String {
	use base64::{engine::general_purpose as b64, Engine as _};
	use sha2::{Digest, Sha256};
	let mut hash = Sha256::new();
	hash.update(challenge.as_bytes());
	let result = hash.finalize();
	b64::URL_SAFE_NO_PAD.encode(result)
}