Remove deprecated setting of ssl_context

Raise an exception if both a proxy_ssl_context and a ssl_context
are provided when use_forwarding_for_https=True, instead of
only raising a warning.

Modify tests to account for change.

Resolves urllib3#2577

changelog/2577.bugfix.rst

@@ -2,5 +2,5 @@ The ``proxy_ssl_context`` argument for ``urllib3.ProxyManager`` will be used
 for the connection to the proxy when the connection is forwarded, either because
 ``use_forwarding_for_https`` is set to ``True`` or because the target is a HTTP destination.
 Previously, ``proxy_ssl_context`` was not used in these situations. If ``ssl_context``
-is passed as a keyword argument, it will be used if ``proxy_ssl_context`` is not set,
-but this use is deprecated.
+was passed as a keyword argument, it had been used if ``proxy_ssl_context`` were not set,
+but setting ``ssl_context`` will now raise an error.

src/urllib3/connection.py

@@ -424,26 +424,16 @@ def __init__(
 
         if proxy_config and proxy_config.use_forwarding_for_https:
             if proxy_config.ssl_context is not None and ssl_context is not None:
-                warnings.warn(
-                    "The 'ssl_context' parameter is not used to configure the connection to the proxy when the 'use_forwarding_for_https' parameter is set to True "
-                    "and should not be set. The 'proxy_ssl_context' parameter is used to configure the connection. "
-                    "In a later urllib3 v2.x release, setting ssl_context will result in an error",
-                    DeprecationWarning,
-                    stacklevel=2,
+                raise ValueError(
+                    "The 'ssl_context' parameter cannot be set when use_forwarding_for_https is True"
                 )
             elif proxy_config.ssl_context is None and ssl_context is not None:
-                warnings.warn(
-                    "The 'ssl_context' parameter should not be used to configure the connection to the proxy when the 'use_forwarding_for_https' parameter is set to True, "
-                    "Use the 'proxy_ssl_context' parameter to customize the connection. "
-                    "In a later urllib3 v2.x release, setting ssl_context will result in an error",
-                    DeprecationWarning,
-                    stacklevel=2,
-                )
-                self.proxy_config = ProxyConfig(
-                    ssl_context, proxy_config.use_forwarding_for_https
+                raise ValueError(
+                    "The 'ssl_context' parameter cannot be set when use_forwarding_for_https is True. Use the 'proxy_ssl_context' parameter to customize the connection to the proxy"
                 )
+            else:
 
-            self.ssl_context = proxy_config.ssl_context
+                self.ssl_context = proxy_config.ssl_context
         else:
             self.ssl_context = ssl_context
 

test/with_dummyserver/test_proxy_poolmanager.py

@@ -426,7 +426,9 @@ def test_forwarding_for_https_error_with_ssl_ctx(self) -> None:
             use_forwarding_for_https=True,
             ssl_context=ctx,
         ) as proxy:
-            with pytest.warns(DeprecationWarning):
+            with pytest.raises(
+                ValueError, match="The 'ssl_context' parameter cannot be set"
+            ):
                 proxy.request("GET", self.https_url)
 
     def test_forwarding_for_https_error_with_only_ssl_ctx(self) -> None:
@@ -435,7 +437,9 @@ def test_forwarding_for_https_error_with_only_ssl_ctx(self) -> None:
         with proxy_from_url(
             self.https_proxy_url, use_forwarding_for_https=True, ssl_context=ctx
         ) as proxy:
-            with pytest.warns(DeprecationWarning):
+            with pytest.raises(
+                ValueError, match="The 'ssl_context' parameter cannot be set"
+            ):
                 proxy.request("GET", self.https_url)
 
     def test_headerdict(self) -> None: