[BE] Fix encoding of classroom credentials

backend/src/online_classroom/session.rs

@@ -1,5 +1,6 @@
 use chrono::{DateTime, Local, TimeZone, Utc};
 use lazy_static::lazy_static;
+use urlencoding::encode;
 use std::time::{SystemTime, UNIX_EPOCH};
 
 use isahc::{cookies::CookieJar, prelude::*, Request};
@@ -188,7 +189,8 @@ async fn login() -> Result<(), String> {
         .cookie_jar(jar.clone())
         .body(format!(
             "login={}&password={}&submitAuth=&_qf__formLogin=",
-            classroom_user, classroom_password
+            encode(classroom_user.as_str()),
+            encode(classroom_password.as_str()),
         ))
         .unwrap()
         .send();