Search with messaging extensions to get searched user details

Hello Team,

I would like to know how to get the searched user details (means which user searching for data) in "Search with message extension", which I implemented like https://docs.microsoft.com/en-us/microsoftteams/platform/resources/messaging-extension-v3/search-extensions

using C#, same as https://github.com/microsoft/BotBuilder-Samples/tree/main/samples/csharp_dotnetcore/50.teams-messaging-extensions-search

and I tried these all https://docs.microsoft.com/en-us/microsoftteams/platform/bots/how-to/get-teams-context?tabs=dotnet which are showing forbidden or object not set to instance of object.

How to get user details in C# for search based messaging extension ?? I required userPrincipalName

Thanks, 

Surya.