I conducted some further research. To enable access to the CredentialManager API in a WPF application the following snippet should be added to the .csproj file (inside the <Project> node):
<ItemGroup>
<Reference Include="System.Runtime.WindowsRuntime, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089, processorArchitecture=MSIL">
<SpecificVersion>False</SpecificVersion>
<HintPath>$(MSBuildProgramFiles32)\Reference Assemblies\Microsoft\Framework\.NETCore\v4.5\System.Runtime.WindowsRuntime.dll</HintPath>
</Reference>
<Reference Include="Windows">
<HintPath>$(MSBuildProgramFiles32)\Windows Kits\10\UnionMetadata\Facade\Windows.WinMD</HintPath>
</Reference>
<Reference Include="Windows.Foundation.FoundationContract">
<HintPath>$(MSBuildProgramFiles32)\Windows Kits\10\References\Windows.Foundation.FoundationContract\1.0.0.0\Windows.Foundation.FoundationContract.winmd</HintPath>
</Reference>
<Reference Include="Windows.Foundation.UniversalApiContract">
<HintPath>$(MSBuildProgramFiles32)\Windows Kits\10\References\Windows.Foundation.UniversalApiContract\1.0.0.0\Windows.Foundation.UniversalApiContract.winmd</HintPath>
</Reference>
</ItemGroup>
With these references, I was able to add Windows Hello to a WPF application. Conversion to a Store-app via the Centennial bridge isn't required in this case.
Hope this helps a bit!