Make `Algorithm` an abstract base class (#845)

* Make `Algorithm` an abstract base class

This also removes some tests that are not relevant anymore

Raise `NotImplementedError` for `NoneAlgorithm`

* Use `hasattr` instead of `getattr`

* Only allow `dict` in `encode`

2 files changed, 23 insertions, 14 deletions

diff --git a/jwt/algorithms.py b/jwt/algorithms.py
index 277f940..bc928fe 100644
--- a/jwt/algorithms.py
+++ b/jwt/algorithms.py
@@ -1,6 +1,7 @@
 import hashlib
 import hmac
 import json
+from abc import ABC, abstractmethod
 from typing import Any, ClassVar, Dict, Type, Union
 
 from .exceptions import InvalidKeyError
@@ -117,7 +118,7 @@ def get_default_algorithms() -> Dict[str, "Algorithm"]:
     return default_algorithms
 
 
-class Algorithm:
+class Algorithm(ABC):
     """
     The interface for an algorithm used to sign and verify tokens.
     """
@@ -148,40 +149,40 @@ class Algorithm:
     #       variadic (TypeVar) but as discussed in https://github.com/jpadilla/pyjwt/pull/605
     #       that may still be poorly supported.
 
+    @abstractmethod
     def prepare_key(self, key: Any) -> Any:
         """
         Performs necessary validation and conversions on the key and returns
         the key value in the proper format for sign() and verify().
         """
-        raise NotImplementedError
 
+    @abstractmethod
     def sign(self, msg: bytes, key: Any) -> bytes:
         """
         Returns a digital signature for the specified message
         using the specified key value.
         """
-        raise NotImplementedError
 
+    @abstractmethod
     def verify(self, msg: bytes, key: Any, sig: bytes) -> bool:
         """
         Verifies that the specified digital signature is valid
         for the specified message and key values.
         """
-        raise NotImplementedError
 
     @staticmethod
+    @abstractmethod
     def to_jwk(key_obj) -> JWKDict:
         """
         Serializes a given RSA key into a JWK
         """
-        raise NotImplementedError
 
     @staticmethod
+    @abstractmethod
     def from_jwk(jwk: JWKDict):
         """
         Deserializes a given RSA key from JWK back into a PublicKey or PrivateKey object
         """
-        raise NotImplementedError
 
 
 class NoneAlgorithm(Algorithm):
@@ -205,6 +206,14 @@ class NoneAlgorithm(Algorithm):
     def verify(self, msg, key, sig):
         return False
 
+    @staticmethod
+    def to_jwk(key_obj) -> JWKDict:
+        raise NotImplementedError()
+
+    @staticmethod
+    def from_jwk(jwk: JWKDict):
+        raise NotImplementedError()
+
 
 class HMACAlgorithm(Algorithm):
     """
@@ -299,7 +308,7 @@ if has_crypto:
         def to_jwk(key_obj):
             obj = None
 
-            if getattr(key_obj, "private_numbers", None):
+            if hasattr(key_obj, "private_numbers"):
                 # Private key
                 numbers = key_obj.private_numbers()
 
@@ -316,7 +325,7 @@ if has_crypto:
                     "qi": to_base64url_uint(numbers.iqmp).decode(),
                 }
 
-            elif getattr(key_obj, "verify", None):
+            elif hasattr(key_obj, "verify"):
                 # Public key
                 numbers = key_obj.public_numbers()
 
@@ -587,7 +596,7 @@ if has_crypto:
                 msg,
                 padding.PSS(
                     mgf=padding.MGF1(self.hash_alg()),
-                    salt_length=self.hash_alg.digest_size,
+                    salt_length=self.hash_alg().digest_size,
                 ),
                 self.hash_alg(),
             )
@@ -599,7 +608,7 @@ if has_crypto:
                     msg,
                     padding.PSS(
                         mgf=padding.MGF1(self.hash_alg()),
-                        salt_length=self.hash_alg.digest_size,
+                        salt_length=self.hash_alg().digest_size,
                     ),
                     self.hash_alg(),
                 )
diff --git a/jwt/api_jwt.py b/jwt/api_jwt.py
index 5664949..d85f6e8 100644
--- a/jwt/api_jwt.py
+++ b/jwt/api_jwt.py
@@ -3,7 +3,7 @@ from __future__ import annotations
 import json
 import warnings
 from calendar import timegm
-from collections.abc import Iterable, Mapping
+from collections.abc import Iterable
 from datetime import datetime, timedelta, timezone
 from typing import Any, Dict, List, Optional, Type, Union
 
@@ -47,10 +47,10 @@ class PyJWT:
         json_encoder: Optional[Type[json.JSONEncoder]] = None,
         sort_headers: bool = True,
     ) -> str:
-        # Check that we get a mapping
-        if not isinstance(payload, Mapping):
+        # Check that we get a dict
+        if not isinstance(payload, dict):
             raise TypeError(
-                "Expecting a mapping object, as JWT only supports "
+                "Expecting a dict object, as JWT only supports "
                 "JSON objects as payloads."
             )