.Net: Disable automatic HTTP redirects in HttpPlugin and WebFileDownloadPlugin default clients

[SergeyMenshykh]

The default HTTP clients used by HttpPlugin and WebFileDownloadPlugin now have AllowAutoRedirect set to false. This ensures the AllowedDomains restriction is enforced consistently regardless of server responses.

• Added GetNonRedirectingHttpClient() to HttpClientProvider (all target frameworks)
• Updated both plugins to use non-redirecting clients by default
• Added unit tests verifying redirect responses are not followed
• Updated XML documentation

[github-actions]

Python Test Coverage Report •

File	Stmts	Miss	Cover	Missing
connectors
mcp.py	464	205	55%	81, 86, 98, 108–117, 124–125, 128–129, 138–139, 146, 160–167, 175–179, 181–182, 184, 193, 296–302, 337–339, 344–346, 360–361, 364–365, 373–375, 407–408, 410, 412, 414–420, 424–426, 428–438, 442–443, 447–448, 452, 454, 458–459, 463, 471, 486, 501–509, 528–529, 544–545, 564–565, 568–569, 572–577, 581–582, 585–586, 589–595, 675, 677, 750, 752, 754, 756, 831, 833, 835, 837, 839, 903, 946–951, 953–956, 961, 1014, 1016, 1019, 1033, 1053–1055, 1070–1074, 1077–1080, 1083–1085, 1089–1093, 1096–1097, 1106–1107, 1109–1111, 1125–1126, 1128–1129, 1131–1133, 1136, 1143–1146, 1154, 1159–1164, 1169, 1171, 1174–1176
TOTAL	28901	5653	80%

Python Unit Test Overview

Tests	Skipped	Failures	Errors	Time
4052	23 💤	0 ❌	0 🔥	1m 22s ⏱️

[Copilot]

Pull request overview

This PR tightens security around outbound HTTP usage by ensuring Semantic Kernel’s built-in web plugins don’t automatically follow HTTP redirects, preventing redirect-based bypasses of the domain allow-list. It also adds a Python MCP server hardening change to enforce excluded tools at call time.

Changes:

• .NET: Introduces HttpClientProvider.GetNonRedirectingHttpClient() and switches HttpPlugin / WebFileDownloadPlugin default constructors to use non-redirecting clients.
• .NET: Adds unit tests intended to verify redirect responses are not followed.
• Python: Enforces excluded_functions at MCP call time (not only by omitting them from tool listings) and adds a unit test for that behavior.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
python/tests/unit/connectors/mcp/test_mcp.py	Adds a unit test asserting excluded MCP tools cannot be invoked.
python/semantic_kernel/connectors/mcp.py	Enforces excluded tool names at call time by raising an MCP “method not found” error.
dotnet/src/Plugins/Plugins.Web/WebFileDownloadPlugin.cs	Switches default HTTP client to non-redirecting and updates XML docs to clarify redirect behavior.
dotnet/src/Plugins/Plugins.UnitTests/Web/WebFileDownloadPluginTests.cs	Adds a redirect-related test for file downloads.
dotnet/src/Plugins/Plugins.UnitTests/Core/HttpPluginTests.cs	Adds a redirect-related test for HttpPlugin.
dotnet/src/Plugins/Plugins.Core/HttpPlugin.cs	Switches default HTTP client to non-redirecting and updates XML docs to clarify redirect behavior.
dotnet/src/InternalUtilities/src/Http/HttpClientProvider.cs	Adds a non-redirecting HttpClient factory backed by a handler with AllowAutoRedirect = false.

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