Get a parameter when the application is launched with a protocol

Question

Hello,

I have a protocol that allows me to launch my application from a browser as follows: myapp:blablabla

The application starts correctly, but how do I get the value "blablabla" in my application ?

Another example is the popular gaming platform Steam, if you put url bar "steam: connect 255.255.255.255:27015" Steam retrieve the command and it automatically connect to the server.

Thank you in advance