Add client connection error exception (#876)

This change adds a new `PyJWKClientConnectionError` exception which
helps to differentiate connection errors from other types of failures
when calling methods such as `get_signing_key_from_jwt()`. This allows
users to do things like retry the method if there's a connection issue.

3 files changed, 18 insertions, 3 deletions

diff --git a/jwt/exceptions.py b/jwt/exceptions.py
index dbe0056..8ac6ecf 100644
--- a/jwt/exceptions.py
+++ b/jwt/exceptions.py
@@ -64,3 +64,7 @@ class PyJWKSetError(PyJWTError):
 
 class PyJWKClientError(PyJWTError):
     pass
+
+
+class PyJWKClientConnectionError(PyJWKClientError):
+    pass
diff --git a/jwt/jwks_client.py b/jwt/jwks_client.py
index e237186..7cecfbf 100644
--- a/jwt/jwks_client.py
+++ b/jwt/jwks_client.py
@@ -6,7 +6,7 @@ from urllib.error import URLError
 
 from .api_jwk import PyJWK, PyJWKSet
 from .api_jwt import decode_complete as decode_token
-from .exceptions import PyJWKClientError
+from .exceptions import PyJWKClientConnectionError, PyJWKClientError
 from .jwk_set_cache import JWKSetCache
 
 
@@ -51,7 +51,9 @@ class PyJWKClient:
             with urllib.request.urlopen(r, timeout=self.timeout) as response:
                 jwk_set = json.load(response)
         except (URLError, TimeoutError) as e:
-            raise PyJWKClientError(f'Fail to fetch data from the url, err: "{e}"')
+            raise PyJWKClientConnectionError(
+                f'Fail to fetch data from the url, err: "{e}"'
+            )
         else:
             return jwk_set
         finally:
diff --git a/tests/test_jwks_client.py b/tests/test_jwks_client.py
index 5886c6a..1122af8 100644
--- a/tests/test_jwks_client.py
+++ b/tests/test_jwks_client.py
@@ -9,7 +9,7 @@ import pytest
 import jwt
 from jwt import PyJWKClient
 from jwt.api_jwk import PyJWK
-from jwt.exceptions import PyJWKClientError
+from jwt.exceptions import PyJWKClientConnectionError, PyJWKClientError
 
 from .utils import crypto_required
 
@@ -283,6 +283,15 @@ class TestPyJWKClient:
 
             assert jwks_client.jwk_set_cache is None
 
+    def test_failed_request_should_raise_connection_error(self):
+        token = "eyJ0eXAiOiJKV1QiLCJhbGciOiJSUzI1NiIsImtpZCI6Ik5FRTFRVVJCT1RNNE16STVSa0ZETlRZeE9UVTFNRGcyT0Rnd1EwVXpNVGsxUWpZeVJrUkZRdyJ9.eyJpc3MiOiJodHRwczovL2Rldi04N2V2eDlydS5hdXRoMC5jb20vIiwic3ViIjoiYVc0Q2NhNzl4UmVMV1V6MGFFMkg2a0QwTzNjWEJWdENAY2xpZW50cyIsImF1ZCI6Imh0dHBzOi8vZXhwZW5zZXMtYXBpIiwiaWF0IjoxNTcyMDA2OTU0LCJleHAiOjE1NzIwMDY5NjQsImF6cCI6ImFXNENjYTc5eFJlTFdVejBhRTJINmtEME8zY1hCVnRDIiwiZ3R5IjoiY2xpZW50LWNyZWRlbnRpYWxzIn0.PUxE7xn52aTCohGiWoSdMBZGiYAHwE5FYie0Y1qUT68IHSTXwXVd6hn02HTah6epvHHVKA2FqcFZ4GGv5VTHEvYpeggiiZMgbxFrmTEY0csL6VNkX1eaJGcuehwQCRBKRLL3zKmA5IKGy5GeUnIbpPHLHDxr-GXvgFzsdsyWlVQvPX2xjeaQ217r2PtxDeqjlf66UYl6oY6AqNS8DH3iryCvIfCcybRZkc_hdy-6ZMoKT6Piijvk_aXdm7-QQqKJFHLuEqrVSOuBqqiNfVrG27QzAPuPOxvfXTVLXL2jek5meH6n-VWgrBdoMFH93QEszEDowDAEhQPHVs0xj7SIzA"
+        url = "https://dev-87evx9ru.auth0.com/.well-known/jwks.json"
+
+        jwks_client = PyJWKClient(url)
+        with pytest.raises(PyJWKClientConnectionError):
+            with mocked_failed_response():
+                jwks_client.get_signing_key_from_jwt(token)
+
     def test_get_jwt_set_refresh_cache(self):
         url = "https://dev-87evx9ru.auth0.com/.well-known/jwks.json"
         jwks_client = PyJWKClient(url)