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SYSLIB0009: AuthenticationManager is not supported

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The following APIs are marked obsolete, starting in .NET 5. Use of these APIs generates warning SYSLIB0009 at compile time and throws a PlatformNotSupportedException at run time.

In .NET 9 and later versions, the entire AuthenticationManager class is marked obsolete. Use of this class generates warning SYSLIB0009 at compile time. The methods in this class either no-op or throw a PlatformNotSupportedException at run time.

Workarounds

Implement IAuthenticationModule, which has methods that were previously called by AuthenticationManager.Authenticate.

Suppress a warning

If you must use the obsolete APIs, you can suppress the warning in code or in your project file.

To suppress only a single violation, add preprocessor directives to your source file to disable and then re-enable the warning.

// Disable the warning.
#pragma warning disable SYSLIB0009

// Code that uses obsolete API.
// ...

// Re-enable the warning.
#pragma warning restore SYSLIB0009

To suppress all the SYSLIB0009 warnings in your project, add a <NoWarn> property to your project file.

<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
   ...
   <NoWarn>$(NoWarn);SYSLIB0009</NoWarn>
  </PropertyGroup>
</Project>

For more information, see Suppress warnings.