Use the old JSONEncoder from flask as a default

Created a copy of the deprecated JSONEncoder used by flask and use this
as a default for PyJWT. This might break for some installations which
further extended the flask provided JSONEncoder. To get this working
again the extension must be adjusted such that a custom Encoder can be
configured.

flask_jwt_extended/config.py

@@ -1,6 +1,8 @@
+import json
 from datetime import datetime
 from datetime import timedelta
 from datetime import timezone
+from typing import Any
 from typing import Iterable
 from typing import List
 from typing import Optional
@@ -9,12 +11,37 @@
 from typing import Union
 
 from flask import current_app
-from flask.json import JSONEncoder
+from flask.json.provider import _default
 from jwt.algorithms import requires_cryptography
 
 from flask_jwt_extended.typing import ExpiresDelta
 
 
+class JSONEncoder(json.JSONEncoder):
+    """The default JSON encoder. Handles extra types compared to the
+    built-in :class:`json.JSONEncoder`.
+
+    -   :class:`datetime.datetime` and :class:`datetime.date` are
+        serialized to :rfc:`822` strings. This is the same as the HTTP
+        date format.
+    -   :class:`decimal.Decimal` is serialized to a string.
+    -   :class:`uuid.UUID` is serialized to a string.
+    -   :class:`dataclasses.dataclass` is passed to
+        :func:`dataclasses.asdict`.
+    -   :class:`~markupsafe.Markup` (or any object with a ``__html__``
+        method) will call the ``__html__`` method to get a string.
+
+    """
+
+    def default(self, o: Any) -> Any:
+        """Convert ``o`` to a JSON serializable type. See
+        :meth:`json.JSONEncoder.default`. Python does not support
+        overriding how basic types like ``str`` or ``list`` are
+        serialized, they are handled before this method.
+        """
+        return _default(o)
+
+
 class _Config(object):
     """
     Helper object for accessing and verifying options in this extension. This
@@ -284,7 +311,7 @@ def error_msg_key(self) -> str:
 
     @property
     def json_encoder(self) -> Type[JSONEncoder]:
-        return current_app.json_encoder
+        return JSONEncoder
 
     @property
     def decode_audience(self) -> Union[str, Iterable[str]]:

tests/test_config.py

@@ -3,7 +3,6 @@
 import pytest
 from dateutil.relativedelta import relativedelta
 from flask import Flask
-from flask.json import JSONEncoder
 
 from flask_jwt_extended import JWTManager
 from flask_jwt_extended.config import config
@@ -65,8 +64,6 @@ def test_default_configs(app):
 
         assert config.identity_claim_key == "sub"
 
-        assert config.json_encoder is app.json_encoder
-
         assert config.error_msg_key == "msg"
 
 
@@ -112,11 +109,6 @@ def test_override_configs(app, delta_func):
 
     app.config["JWT_ERROR_MESSAGE_KEY"] = "message"
 
-    class CustomJSONEncoder(JSONEncoder):
-        pass
-
-    app.json_encoder = CustomJSONEncoder
-
     with app.test_request_context():
         assert config.token_location == ["cookies", "query_string", "json"]
         assert config.jwt_in_query_string is True
@@ -162,8 +154,6 @@ class CustomJSONEncoder(JSONEncoder):
 
         assert config.identity_claim_key == "foo"
 
-        assert config.json_encoder is CustomJSONEncoder
-
         assert config.error_msg_key == "message"