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: config.rs
    path of file: ./repos/tiny/crates/tiny/src
    
    the code of the file until where you have to start completion: use libtiny_client::SASLAuth as ClientSASLAuth;
use serde::{Deserialize, Deserializer};

use std::fs;
use std::fs::File;
use std::io::{Read, Write};
use std::path::{Path, PathBuf};
use std::process::Command;

use libtiny_tui::config::Chan;

#[derive(Clone, Deserialize, Debug, PartialEq, Eq)]
#[serde(untagged, rename_all = "snake_case")]
pub(crate) enum SASLAuth<P> {
    Plain {
        /// Registered username
        username: String,
        /// Password
        password: P,
    },
    External {
        /// Path to PE
    
    pub(crate) fn read_passwords(self) -> Option<Config<String>> {
        let Config {
            servers,
            defaults,
            log_dir,
        } = self;

        let mut servers_: Vec<Server<String>> = Vec::with_capacity(servers.len());

        for server in servers {
            let Server {
                addr,
                alias,
                port,
                tls,
                pass,
                realname,
                nicks,
                join,
                nickserv_ident,
                sasl_auth,
            } = server;

            let pass = match pass {
                None => None,
                Some(PassOrCmd::Pass(pass)) => Some(pass),
                Some(PassOrCmd::Cmd(cmd)) => Some(run_command("server password", &addr, &cmd)?),
            };

            let nickserv_ident = match nickserv_ident {
                None => None,
                Some(PassOrCmd::Pass(pass)) => Some(pass),
                Some(PassOrCmd::Cmd(cmd)) => Some(run_command("NickServ password", &addr, &cmd)?),
            };

            let sasl_auth = match sasl_auth {
                None => None,
                Some(SASLAuth::Plain {
                    username,
                    password: PassOrCmd::Pass(pass),
                }) => Some(SASLAuth::Plain {
                    username,
                    password: pass,
                }),
                Some(SASLAuth::Plain {
                    username,
                    password: PassOrCmd::Cmd(cmd),
                }) => {
                    let password = run_command("SASL password", &addr, &cmd)?;
                    Some(SASLAuth::Plain { username, password })
                }
                Some(SASLAuth::External { pem }) => Some(SASLAuth::External { pem }),
            };

            servers_.push(Server {
                addr,
                alias,
                port,
                tls,
                pass,
                realname,
                nicks,
                join,
                nickserv_ident,
                sasl_auth,
            });
        }

        Some(Config {
            servers: servers_,
            defaults,
            log_dir,
        })
    }