Simplify authentication logic for EIP1271.

nucypher/policy/conditions/auth/evm.py

@@ -164,6 +164,52 @@ class EIP1271Auth(EvmAuth):
     MAGIC_VALUE_BYTES = bytes(HexBytes("0x1626ba7e"))
     LOG = Logger("EIP1271Auth")
 
+    @classmethod
+    def _extract_typed_data(cls, data):
+        try:
+            data_hash = bytes(HexBytes(data["dataHash"]))
+            chain = data["chain"]
+            return data_hash, chain
+        except Exception as e:
+            # data could not be processed
+            raise cls.InvalidData(
+                f"Invalid EIP1271 authentication data: {str(e) or e.__class__.__name__}"
+            )
+
+    @classmethod
+    def _validate_auth_data(
+        cls, data_hash, signature_bytes, expected_address, chain, providers
+    ):
+        web3_endpoints = providers.web3_endpoints(chain_id=chain)
+        last_error = None
+        for web3_instance in web3_endpoints:
+            try:
+                # Interact with the EIP1271 contract
+                eip1271_contract = web3_instance.eth.contract(
+                    address=expected_address, abi=cls.EIP1271_ABI
+                )
+                result = eip1271_contract.functions.isValidSignature(
+                    data_hash,
+                    signature_bytes,
+                ).call()
+                if result == cls.MAGIC_VALUE_BYTES:
+                    return  # Successful authentication
+
+                break
+            except Exception as e:
+                last_error = f"EIP1271 contract call failed ({expected_address}): {e}"
+                cls.LOG.warn(f"{last_error}; attempting next provider")
+        else:
+            # If all providers fail
+            if last_error:
+                raise cls.AuthenticationFailed(
+                    f"EIP1271 verification failed; {last_error}"
+                )
+
+        raise cls.AuthenticationFailed(
+            f"EIP1271 verification failed; signature not valid for contract address, {expected_address}"
+        )
+
     @classmethod
     def authenticate(
         cls,
@@ -172,46 +218,27 @@ class EIP1271Auth(EvmAuth):
         expected_address: ChecksumAddress,
         providers: Optional[ConditionProviderManager] = None,
     ):
-        try:
-            data_hash = bytes(HexBytes(data["dataHash"]))
-            chain = data["chain"]
-            signature_bytes = bytes(HexBytes(signature))
-            w3_instances = providers.web3_endpoints(chain_id=chain)
+        if not providers:
+            # should never happen
+            raise cls.AuthenticationFailed(
+                "EIP1271 verification failed; no endpoints provided"
+            )
 
-            latest_error = ""
-            for w3 in w3_instances:
-                try:
-                    eip1271_contract = w3.eth.contract(
-                        address=expected_address, abi=cls.EIP1271_ABI
-                    )
-                    result = eip1271_contract.functions.isValidSignature(
-                        data_hash,
-                        signature_bytes,
-                    ).call()
-                    if result == cls.MAGIC_VALUE_BYTES:
-                        return  # Authentication successful
-                    break
-                except Exception as e:
-                    latest_error = (
-                        f"EIP1271 contract call failed ({expected_address}): {e}"
-                    )
-                    cls.LOG.warn(f"{latest_error}; attempting next provider")
-            else:
-                raise cls.AuthenticationFailed(
-                    f"EIP1271 verification failed; {latest_error}"
-                )
+        # Extract and validate input data
+        data_hash, chain = cls._extract_typed_data(data)
+
+        # Validate the signature
+        signature_bytes = bytes(HexBytes(signature))
+        try:
+            cls._validate_auth_data(
+                data_hash, signature_bytes, expected_address, chain, providers
+            )
         except NoConnectionToChain:
             raise cls.AuthenticationFailed(
-                f"EIP1271 verification failed; No connection to chain ID {data['chain']}"
+                f"EIP1271 verification failed; No connection to chain ID {chain}"
             )
         except cls.AuthenticationFailed:
             raise
         except Exception as e:
-            # data could not be processed
-            raise cls.InvalidData(
-                f"Invalid EIP1271 authentication data: {str(e) or e.__class__.__name__}"
-            )
-
-        raise cls.AuthenticationFailed(
-            f"EIP1271 verification failed; signature not valid for contract address, {expected_address}"
-        )
+            # catch all
+            raise cls.AuthenticationFailed(f"EIP1271 verification failed; {e}")

tests/unit/conditions/test_evm_auth.py

@@ -345,6 +345,12 @@ def test_authenticate_eip1271(mocker, get_random_checksum_address):
         address=eip1271_mock_contract.address, abi=EIP1271Auth.EIP1271_ABI
     )
 
+    # no providers
+    with pytest.raises(EvmAuth.AuthenticationFailed, match="no endpoints provided"):
+        EIP1271Auth.authenticate(
+            typedData, valid_message_signature, eip1271_mock_contract.address, None
+        )
+
     # invalid typed data - no chain id
     with pytest.raises(EvmAuth.InvalidData):
         EIP1271Auth.authenticate(