Ensure that calls to json.dumps are compatible with the standard library json. (#7836)

synapse/handlers/ui_auth/checkers.py

@@ -12,6 +12,7 @@
 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 # See the License for the specific language governing permissions and
 # limitations under the License.
+
 import logging
 
 from canonicaljson import json
@@ -117,7 +118,7 @@ class RecaptchaAuthChecker(UserInteractiveAuthChecker):
         except PartialDownloadError as pde:
             # Twisted is silly
             data = pde.response
-            resp_body = json.loads(data)
+            resp_body = json.loads(data.decode("utf-8"))
 
         if "success" in resp_body:
             # Note that we do NOT check the hostname here: we explicitly