How can I conditionally hide the web methods? I don't want to expose the web method if a flag setup in web.config is false. If it is true, then I will expose the web method.
Meaning: The method should only be visible to the client if the flag is true otherwise it should not be available for the client.
Is this possible in C#?
You can check the flag in your method and throw an exception if it's not set.
You can't really do this.
Your clients "see" the web methods because they are listed in the WSDL. The WSDL generation is fairly static - it is based on the [WebMethod] attributes on your methods. There is really no ability to remove items from the generated WSDL.
If you can switch to WCF, you will find this much, much, easier. In the meantime, you'll just have to use authorization - prevent some clients from calling some methods.
来源：https://stackoverflow.com/questions/5541045/hide-asmx-web-methods-conditionally-in-c-sharp