Add method to Mono library

I'm trying to run an existing web project in Mono that uses version 4.5 of the .NET framework. I am using xsp4 to run this through Mono. I am facing an error when trying to access a website on localhost:

Missing method System.Web.HttpApplication::RegisterModule(Type) in assembly /Library/Frameworks/Mono.framework/Versions/3.8.0/lib/mono/gac/System.Web/4.0.0.0__b03f5f7f11d50a3a/System.Web.dll, referenced in assembly /private/var/folders/xw/1k49vb85533_tl4rn3t6tygw0000gn/T/calvinfroedge-temp-aspnet-0/e60f00e7/assembly/shadow/df4b0596/f4b9d264_2bf2d7f2_00000001/Microsoft.Owin.Host.SystemWeb.dll

      

        
        
        
      

    

I know the problem is the missing "RegisterModule" method in "System.Web.HttpApplication". My question is how can I add this method to the Mono source on my computer and recompile so that the method appears in this file:

/Library/Frameworks/Mono.framework/Versions/3.8.0/lib/mono/gac/System.Web/4.0.0.0__b03f5f7f11d50a3a/System.Web.dll