Add config for setting the recaptcha verify api endpoint, so we can test it in sytest

synapse/config/captcha.py

@@ -26,6 +26,7 @@ class CaptchaConfig(Config):
             config["captcha_ip_origin_is_x_forwarded"]
         )
         self.captcha_bypass_secret = config.get("captcha_bypass_secret")
+        self.recaptcha_siteverify_api = config["recaptcha_siteverify_api"]
 
     def default_config(self, config_dir_path, server_name):
         return """\
@@ -48,4 +49,7 @@ class CaptchaConfig(Config):
 
         # A secret key used to bypass the captcha test entirely.
         #captcha_bypass_secret: "YOUR_SECRET_HERE"
+
+        # The API endpoint to use for verifying m.login.recaptcha responses.
+        recaptcha_siteverify_api: "https://www.google.com/recaptcha/api/siteverify"
         """

synapse/handlers/auth.py

@@ -187,8 +187,8 @@ class AuthHandler(BaseHandler):
         # each request
         try:
             client = SimpleHttpClient(self.hs)
-            data = yield client.post_urlencoded_get_json(
-                "https://www.google.com/recaptcha/api/siteverify",
+            resp_body = yield client.post_urlencoded_get_json(
+                self.hs.config.recaptcha_siteverify_api,
                 args={
                     'secret': self.hs.config.recaptcha_private_key,
                     'response': user_response,