Process for login into C# Web Forms website from Android/IOS

Hello,

Can I use Web Service developed in C# to enable the Android/IOS Mobile app to login into my C# Web Forms Application. Will it be the correct solution in terms of
1. Security

2. Reliability

I will allow 2 parameters user id and password (password will be encrypted by web service and then web forms application will accept encrypted password) to be filled by Android/IOS application and that web service can be consumed by my Web Forms Application to login. Is there any other alternative way to solve this.

Thanks Anoop