What is SOAP?

SOAP is an XML-based protocol for exchanging information between computers. Although SOAP can be used in a variety of messaging systems and can be delivered via a variety of transport protocols, the main focus of SOAP is Remote Procedure Calls (RPC) transported via HTTP. Like XML-RPC, SOAP is platform independent, and therefore enables diverse applications to communicate with one another.
To get a quick sense of SOAP, here is a sample SOAP request to a weather service (with the HTTP Headers omitted):

xmlns:SOAP-ENV="http://www.w3.org/2001/09/soap-envelope"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:xsd="http://www.w3.org/2001/XMLSchema">


10016



As you can see, the request is slightly more complicated than XML-RPC and makes use of both XML namespaces and XML Schemas. Much like XML-RPC, however, the body of the request specifies both a method name (getWeather), and a list of parameters (zipcode).
Here is a sample SOAP response from the weather service:

xmlns:SOAP-ENV="http://www.w3.org/2001/09/soap-envelope"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:xsd="http://www.w3.org/2001/XMLSchema">

xmlns:ns1="urn:examples:weatherservice"
SOAP-ENV:encodingStyle="http://www.w3.org/2001/09/soap-encoding">
*65
*
*
*
The response indicates a single integer return value (the current temperature).
The World Wide Web Consortium (W3C) is in the process of creating a SOAP standard. The latest working draft is designated as SOAP 1.2, and the specification is now broken into two parts. Part 1 describes the SOAP messaging framework and envelope specification. Part 2 describes the SOAP encoding rules, the SOAP-RPC convention, and HTTP binding details.

What is a Web service?

Web service is any piece of software that makes itself available over the Internet and uses a standardized XML messaging system

XML is used to encode all communications to a Web service. For example, a client invokes a Web service by sending an XML message, then waits for a corresponding XML response. Because all communication is in XML, Web services are not tied to any one operating system or programming language--Java can talk with Perl; Windows applications can talk with Unix applications.
Beyond this basic definition, a Web service may also have two additional (and desirable) properties:

First, a Web service can have a public interface, defined in a common XML grammar. The interface describes all the methods available to clients and specifies the signature for each method. Currently, interface definition is accomplished via the Web Service Description Language (WSDL).

Second, if you create a Web service, there should be some relatively simple mechanism for you to publish this fact. Likewise, there should be some simple mechanism for interested parties to locate the service and locate its public interface. The most prominent directory of Web services is currently available via UDDI, or Universal Description, Discovery, and Integration

Send Soap Request Request with Credential using SoapClient

namespace test{
using System;
using System.Collections.Generic;
using System.Text;
using Microsoft.Web.Services3;
using Microsoft.Web.Services3.Addressing;
using Microsoft.Web.Services3.Messaging;
using System.Web.Services.Protocols;
using System.Net;
using System.Web;
using System.Configuration;

class OutgoingSoapClient : SoapClient {

public SoapEnvelope GetResponse()
{
try {
string username = "UserName";
string password = "Password"
distAdd="http://localhost/Service1.ashx"
System.Net.CredentialCache credCache = new System.Net.CredentialCache();
credCache.Add (new Uri(distAdd.ToString()), "Basic", new NetworkCredential(username, password));
SoapHttpOutputChannel httpchannel = (SoapHttpOutputChannel)
this.Channel;
httpchannel.Options.Credentials = credCache;
httpchannel.Options.Timeout = 30000;
SoapEnvelope response = this.SendRequestResponse(action, request);
return response;
}
}
}