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[release/2.1] Fix WinHttpHandler when using authenticating proxies #30212
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This was a regression from .NET Core 2.0 due to PR #28105. Proxy authentication using system default proxy settings that involve a PAC file (either autodiscovery or explicit PAC file) cause a NullReferenceException in WinHttpHandler in the CheckResponseForAuthentication() method. This problem is only discovered when using an authenticating proxy server (any auth scheme) that is discovered using PAC files. This is considered the "system default" proxy. When this occurs, the handler's Proxy property is null and dereferencing it caused the exception. Due to the problems described in #6997, the uri of the proxy can't be determined yet since it is only known to WinHTTP. Fixing #6997 is complicated and impacts performance. However, in most cases, as long as the credentials are a NetworkCredential object, knowing the uri of the proxy is needed. I tested this manually using the steps I described in #30191. I did not add any tests to this PR since they can't be run in CI. However, I am working on a task that will eventually add Enterprise-Scenario testing like this (PAC files, authenticating proxies, etc.) to our systems. Fixes #30191 Contributes to #6997
davidsh
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@dotnet-bot test Outerloop Windows x64 Debug Build |
davidsh
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CI Failures are unrelated. |
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@dotnet-bot test Outerloop Windows x64 Debug Build |
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Port of #30196 to release/2.1
This was a regression from .NET Core 2.0 due to PR #28105.
Proxy authentication using system default proxy settings that involve a PAC file
(either autodiscovery or explicit PAC file) cause a NullReferenceException in WinHttpHandler in the
CheckResponseForAuthentication() method.
This problem is only discovered when using an authenticating proxy server (any auth scheme) that is
discovered using PAC files. This is considered the "system default" proxy. When this occurs, the
handler's Proxy property is null and dereferencing it caused the exception.
Due to the problems described in #6997, the uri of the proxy can't be determined yet since it is only
known to WinHTTP. Fixing #6997 is complicated and impacts performance. However, in most cases, as
long as the credentials are a NetworkCredential object, knowing the uri of the proxy is needed.
I tested this manually using the steps I described in #30191. I did not add any tests to this PR since
they can't be run in CI. However, I am working on a task that will eventually add Enterprise-Scenario
testing like this (PAC files, authenticating proxies, etc.) to our systems.
Fixes #30191
Contributes to #6997