Remove text captchas from Invidious (#5308)

textcaptcha.com seems to be down since April and it does not appear that
service will be restored.

Text captchas can be easily automated using free LLMs, so keeping the
text captcha is more like a gate to create accounts in mass on public
Invidious instances.

It also gives headaches like bots automating account creation to modify
the videos that appear popular page of each instance (since the popular
page is based on the subscriptions of the registered users).

locales/en-US.json

@@ -64,8 +64,6 @@
     "User ID": "User ID",
     "Password": "Password",
     "Time (h:mm:ss):": "Time (h:mm:ss):",
-    "Text CAPTCHA": "Text CAPTCHA",
-    "Image CAPTCHA": "Image CAPTCHA",
     "Sign In": "Sign In",
     "Register": "Register",
     "E-mail": "E-mail",

src/invidious/routes/login.cr

@@ -21,9 +21,6 @@ module Invidious::Routes::Login
     account_type = env.params.query["type"]?
     account_type ||= "invidious"
 
-    captcha_type = env.params.query["captcha"]?
-    captcha_type ||= "image"
-
     templated "user/login"
   end
 
@@ -88,34 +85,14 @@ module Invidious::Routes::Login
         password = password.byte_slice(0, 55)
 
         if CONFIG.captcha_enabled
-          captcha_type = env.params.body["captcha_type"]?
           answer = env.params.body["answer"]?
-          change_type = env.params.body["change_type"]?
-
-          if !captcha_type || change_type
-            if change_type
-              captcha_type = change_type
-            end
-            captcha_type ||= "image"
 
           account_type = "invidious"
-
-            if captcha_type == "image"
           captcha = Invidious::User::Captcha.generate_image(HMAC_KEY)
-            else
-              captcha = Invidious::User::Captcha.generate_text(HMAC_KEY)
-            end
-
-            return templated "user/login"
-          end
 
           tokens = env.params.body.select { |k, _| k.match(/^token\[\d+\]$/) }.map { |_, v| v }
 
-          answer ||= ""
+          if answer
-          captcha_type ||= "image"
-
-          case captcha_type
-          when "image"
             answer = answer.lstrip('0')
             answer = OpenSSL::HMAC.hexdigest(:sha256, HMAC_KEY, answer)
 
@@ -124,27 +101,8 @@ module Invidious::Routes::Login
             rescue ex
               return error_template(400, ex)
             end
-          else # "text"
+          else
-            answer = Digest::MD5.hexdigest(answer.downcase.strip)
+            return templated "user/login"
-
-            if tokens.empty?
-              return error_template(500, "Erroneous CAPTCHA")
-            end
-
-            found_valid_captcha = false
-            error_exception = Exception.new
-            tokens.each do |tok|
-              begin
-                validate_request(tok, answer, env.request, HMAC_KEY, locale)
-                found_valid_captcha = true
-              rescue ex
-                error_exception = ex
-              end
-            end
-
-            if !found_valid_captcha
-              return error_template(500, error_exception)
-            end
           end
         end
 

src/invidious/user/captcha.cr

@@ -4,8 +4,6 @@ struct Invidious::User
   module Captcha
     extend self
 
-    private TEXTCAPTCHA_URL = URI.parse("https://textcaptcha.com")
-
     def generate_image(key)
       second = Random::Secure.rand(12)
       second_angle = second * 30
@@ -60,19 +58,5 @@ struct Invidious::User
         tokens:   {generate_response(answer, {":login"}, key, use_nonce: true)},
       }
     end
-
-    def generate_text(key)
-      response = make_client(TEXTCAPTCHA_URL, &.get("/github.com/iv.org/invidious.json").body)
-      response = JSON.parse(response)
-
-      tokens = response["a"].as_a.map do |answer|
-        generate_response(answer.as_s, {":login"}, key, use_nonce: true)
-      end
-
-      return {
-        question: response["q"].as_s,
-        tokens:   tokens,
-      }
-    end
   end
 end

src/invidious/views/user/login.ecr

@@ -25,44 +25,17 @@
                         <% end %>
 
                         <% if captcha %>
-                            <% case captcha_type when %>
-                            <% when "image" %>
                             <% captcha = captcha.not_nil! %>
                             <img style="width:50%" src='<%= captcha[:question] %>'/>
                             <% captcha[:tokens].each_with_index do |token, i| %>
                                 <input type="hidden" name="token[<%= i %>]" value="<%= HTML.escape(token) %>">
                             <% end %>
-                                <input type="hidden" name="captcha_type" value="image">
                             <label for="answer"><%= translate(locale, "Time (h:mm:ss):") %></label>
                             <input type="text" name="answer" type="text" placeholder="h:mm:ss">
-                            <% else # "text" %>
-                                <% captcha = captcha.not_nil! %>
-                                <% captcha[:tokens].each_with_index do |token, i| %>
-                                    <input type="hidden" name="token[<%= i %>]" value="<%= HTML.escape(token) %>">
-                                <% end %>
-                                <input type="hidden" name="captcha_type" value="text">
-                                <label for="answer"><%= captcha[:question] %></label>
-                                <input type="text" name="answer" type="text" placeholder="<%= translate(locale, "Answer") %>">
-                            <% end %>
 
                             <button type="submit" name="action" value="signin" class="pure-button pure-button-primary">
                                 <%= translate(locale, "Register") %>
                             </button>
-
-                            <% case captcha_type when %>
-                            <% when "image" %>
-                                <label>
-                                    <button type="submit" name="change_type" class="pure-button pure-button-primary" value="text">
-                                        <%= translate(locale, "Text CAPTCHA") %>
-                                    </button>
-                                </label>
-                            <% else # "text" %>
-                                <label>
-                                    <button type="submit" name="change_type" class="pure-button pure-button-primary" value="image">
-                                        <%= translate(locale, "Image CAPTCHA") %>
-                                    </button>
-                                </label>
-                            <% end %>
                         <% else %>
                             <button type="submit" name="action" value="signin" class="pure-button pure-button-primary">
                                 <%= translate(locale, "Sign In") %>/<%= translate(locale, "Register") %>