Fix UseManagedNtlm linker substitutions (#90957)

* Fix UseManagedNtlm linker Substitutions

- Specify the default value (false) for the feature on Linux so the linker runs the substitution when no value was specified by the user.
- Make the `UseManagedNtlm` property public because the linker and IL compiler doesn't support substitution of private properties.
- Add `--ignore-substitutions` switch to ILLink during library build to prevent the substitution with default value taking place.

* Revert unnecessary changes, document _UseManagedNtlm switch

* Set _UseManagedNtlm in NativeAOT integration

* Revert unnecessary change, move default values for trimming properties from NativeAOT targets to ILLink ones

* Fix build

docs/workflow/trimming/feature-switches.md

@@ -32,6 +32,7 @@ configurations but their defaults might vary as any SDK can set the defaults dif
 | _AggressiveAttributeTrimming | System.AggressiveAttributeTrimming | When set to true, aggressively trims attributes to allow for the most size savings possible, even if it could result in runtime behavior changes |
 | JsonSerializerIsReflectionEnabledByDefault | System.Text.Json.JsonSerializer.IsReflectionEnabledByDefault | When set to false, disables using reflection as the default contract resolver in System.Text.Json |
 | EnableGeneratedComInterfaceComImportInterop | System.Runtime.InteropServices.Marshalling.EnableGeneratedComInterfaceComImportInterop | When set to true, enables casting source-generated COM object wrappers to built-in COM-based COM interfaces. |
+| _UseManagedNtlm | System.Net.Security.UseManagedNtlm | When set to true, uses built-in managed implementation of NTLM and SPNEGO algorithm for HTTP, SMTP authentication, and NegotiateAuthentication API instead of system provided GSSAPI implementation. |
 
 Any feature-switch which defines property can be set in csproj file or
 on the command line as any other MSBuild property. Those without predefined property name

src/coreclr/nativeaot/BuildIntegration/Microsoft.NETCore.Native.targets

@@ -280,9 +280,6 @@ The .NET Foundation licenses this file to you under the MIT license.
 
       <IlcArg Condition="$(IlcDisableReflection) == 'true'" Include="--feature:System.Reflection.IsReflectionExecutionAvailable=false" />
 
-      <!-- Linux Bionic doesn't ship GSSAPI, so enable managed implementation -->
-      <IlcArg Condition="'$(_linuxLibcFlavor)' == 'bionic'" Include="--feature:System.Net.Security.UseManagedNtlm=true" />
-
       <!-- The managed debugging support in libraries is unused - trim it -->
       <IlcArg Condition="'$(IlcKeepManagedDebuggerSupport)' != 'true'" Include="--feature:System.Diagnostics.Debugger.IsSupported=false" />
       <IlcArg Condition="'$(UseWindowsThreadPool)' != '' and '$(_targetOS)' == 'win'" Include="--feature:System.Threading.ThreadPool.UseWindowsThreadPool=$(UseWindowsThreadPool)" />

src/tools/illink/src/ILLink.Tasks/build/Microsoft.NET.ILLink.targets

@@ -48,6 +48,10 @@ Copyright (c) .NET Foundation. All rights reserved.
     <_EnableConsumingManagedCodeFromNativeHosting Condition="'$(_EnableConsumingManagedCodeFromNativeHosting)' == ''">false</_EnableConsumingManagedCodeFromNativeHosting>
     <VerifyDependencyInjectionOpenGenericServiceTrimmability Condition="'$(VerifyDependencyInjectionOpenGenericServiceTrimmability)' == ''">true</VerifyDependencyInjectionOpenGenericServiceTrimmability>
     <JsonSerializerIsReflectionEnabledByDefault Condition="'$(JsonSerializerIsReflectionEnabledByDefault)' == ''">false</JsonSerializerIsReflectionEnabledByDefault>
+    <!-- Linux Bionic doesn't ship GSSAPI, so enable managed implementation -->
+    <_UseManagedNtlm Condition="'$(_UseManagedNtlm)' == '' and $(RuntimeIdentifier.StartsWith('linux-bionic'))">true</_UseManagedNtlm>
+    <!-- Trim managed NTLM on Linux when it's not explicitly requested -->
+    <_UseManagedNtlm Condition="'$(_UseManagedNtlm)' == '' and $(RuntimeIdentifier.StartsWith('linux'))">false</_UseManagedNtlm>
   </PropertyGroup>