Message Security with Mutual Certificates for Android & iOS

I would like to ask the following. We have a mobile app both for Android & iOS that exchanges data with a .NET server.

For Android the ksoap2 library is used, while for iOS the Alamofire with AEXML libraries are used.

We would like to enable encryption for the communication between the server and the apps, specifically Message Security with Mutual Certificates (https://docs.microsoft.com/en-us/dotnet/framework/wcf/feature-details/message-security-with-mutual-certificates)

I am not able to find any information how either the Android or the iOS client could encrypt/decrypt the requests/responses.

Can you please provide any relative information?

Thanks in advance!

from Message Security with Mutual Certificates for Android & iOS