allow api endpoint '/api/v1/auth/tokens/register' to answer json requ…

…ests with json response

src/invidious/routes/api/v1/authenticated.cr

@@ -398,7 +398,8 @@ module Invidious::Routes::API::V1::Authenticated
     user = env.get("user").as(User)
     locale = env.get("preferences").as(Preferences).locale
 
-    case env.request.headers["Content-Type"]?
+    content_type = env.request.headers["Content-Type"]?
+    case content_type
     when "application/x-www-form-urlencoded"
       scopes = env.params.body.select { |k, _| k.match(/^scopes\[\d+\]$/) }.map { |_, v| v }
       callback_url = env.params.body["callbackUrl"]?
@@ -419,7 +420,7 @@ module Invidious::Routes::API::V1::Authenticated
       callback_url = URI.parse(callback_url)
     end
 
-    if sid = env.get?("sid").try &.as(String)
+    if sid = env.get?("sid").try &.as(String) && content_type != "application/json"
       env.response.content_type = "text/html"
 
       csrf_token = generate_response(sid, {":authorize_token"}, HMAC_KEY, use_nonce: true)