You would have to bypass the Authorization header to do this i.e.
Pass the token or whatever via an alternative header attribute e.g. access-key
You will need to make the service anonymous and then use the service pub.flow:getTransportInfo to get hold of the headers.
As Nagendra indicated, be careful as you are bypassing the built-in security and will need to make sure that your code is water tight. What is your use case for doing this programatically ? it might be possible to combine both.
regards,
John.
#webMethods#Integration-Server-and-ESB