Dont allow caching captcha response (#4381)

Co-authored-by: Dessalines <dessalines@users.noreply.github.com>

crates/api/src/local_user/get_captcha.rs

@@ -1,5 +1,13 @@
 use crate::captcha_as_wav_base64;
-use actix_web::web::{Data, Json};
+use actix_web::{
+  http::{
+    header::{CacheControl, CacheDirective},
+    StatusCode,
+  },
+  web::{Data, Json},
+  HttpResponse,
+  HttpResponseBuilder,
+};
 use captcha::{gen, Difficulty};
 use lemmy_api_common::{
   context::LemmyContext,
@@ -12,13 +20,13 @@ use lemmy_db_schema::source::{
 use lemmy_utils::error::LemmyError;
 
 #[tracing::instrument(skip(context))]
-pub async fn get_captcha(
-  context: Data<LemmyContext>,
-) -> Result<Json<GetCaptchaResponse>, LemmyError> {
+pub async fn get_captcha(context: Data<LemmyContext>) -> Result<HttpResponse, LemmyError> {
   let local_site = LocalSite::read(&mut context.pool()).await?;
+  let mut res = HttpResponseBuilder::new(StatusCode::OK);
+  res.insert_header(CacheControl(vec![CacheDirective::NoStore]));
 
   if !local_site.captcha_enabled {
-    return Ok(Json(GetCaptchaResponse { ok: None }));
+    return Ok(res.json(Json(GetCaptchaResponse { ok: None })));
   }
 
   let captcha = gen(match local_site.captcha_difficulty.as_str() {
@@ -37,11 +45,12 @@ pub async fn get_captcha(
   // Stores the captcha item in the db
   let captcha = CaptchaAnswer::insert(&mut context.pool(), &captcha_form).await?;
 
-  Ok(Json(GetCaptchaResponse {
+  let json = Json(GetCaptchaResponse {
     ok: Some(CaptchaResponse {
       png,
       wav,
       uuid: captcha.uuid.to_string(),
     }),
-  }))
+  });
+  Ok(res.json(json))
 }