LibSOAP

Web services (SOAP) library

Library for working with web services and WSDL files. Version 1.4 allows the use of either web-based urls and disk-based files for wsdls, adds a function to list the available web services at a site, works with more wsdl schemas, and produces better prototypes.

Click the Usage button, and then the script of the DoIt button has a call to convert from Fahrenheit to Celsius. It's a pretty simple example, just one parameter, and doesn't need to set any authentication headers. But hopefully that will give you a start as to how to proceed.