SOAP Web Service API in PHP

Question

I am attempting to interrogate a SOAP API using a web service in PHP:

The web service simply lists the available datasets and the fields which those datasets contain. The web service takes no parameters, but does require authentication.

<soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/"; xmlns:v0="http://www.weatherservice.com/service/infrastructure/search/v0-1">;
   <soapenv:Header>
      <v0:HeaderLogin>
         <username>johnsmith</username>
         <password>secretpassword</password>
      </v0:HeaderLogin>
   </soapenv:Header>
   <soapenv:Body>
     <v0:listdatasets/>
   </soapenv:Body>
</soapenv:Envelope>

I don't know where to start tbh, any help would be appreciated.