How-to: Calling Web Services Using Basic Authentication

How-to: WebMethods Call Using Basic Authentication

I recently made a web services call into WebMethods using basic authentication.  This authentication meant that we needed to modify the WSDL-generated classes to handle the authentication.

Here’s how it works.  I add a reference to the Web Service (Visual Studio generates the client code for calling the web service).  Then, to this generated class I need to add the following method:

protected override System.Net.WebRequest GetWebRequest(Uri uri)
{
    HttpWebRequest request;
    request = (HttpWebRequest)base.GetWebRequest(uri);

    if (PreAuthenticate)
    {
        NetworkCredential networkCredentials =
        Credentials.GetCredential(uri, "Basic");

        if (networkCredentials != null)
        {
            byte[] credentialBuffer = new UTF8Encoding().GetBytes(
            networkCredentials.UserName + ":" +
            networkCredentials.Password);
            request.Headers["Authorization"] =
            "Basic " + Convert.ToBase64String(credentialBuffer);
        }
        else
        {
            throw new ApplicationException("No network credentials");
        }
    }
    return request;
}
Code language: PHP (php)

This overrides the GetWebRequest() <code> method of the </code> System.Web.Services.Protocols.SoapHttpClientProtocol class that the web service client code derived from.

With Visual Studio 2005 the generated code is a C# 2.0 partial class.  As a result, regenerating the web services client code does not over-write the additional method.  To enable this, add a class file to your project and give it the same namespace and name as the generated  System.Web.Services.Protocols.SoapHttpClientProtocol <code> derived class.  The key is to use the partial modifier on the class header so that the </code> GetWebRequest() <code> method is added to the generated class.  (</code> partial class Michaelis.MockService{...} )

Regardless of using Visual Studio.NET 2005 or earlier, the client code requires that the network credentials are set and the  PreAuthenticate property is assigned true.  Here is a sample client call:

Michaelis.MockService service = new Michaelis.MockService();

// Create the network credentials and assign
// them to the service credentials
NetworkCredential netCredential = new NetworkCredential("Inigo.Montoya", "Ykmfptd");
Uri uri = new Uri(service.Url);
ICredentials credentials = netCredential.GetCredential(uri, "Basic");
service.Credentials = credentials;

// Be sure to set PreAuthenticate to true or else
// authentication will not be sent.
service.PreAuthenticate = true;

// Make the web service call.
service.Method();
Code language: JavaScript (javascript)

UPDATE for Calling Web Services

Comments on the post raised the question, “Why can’t you just say request.Credentials = new NetworkCredential(username,password).”

The reason relates to interoperating with WebMethods specifically.  When just setting Credentials , the HTTP header looks like this:

POST /soap/rpc HTTP/1.1  
User-Agent: Mozilla/4.0 (compatible; MSIE 6.0; MS Web Services Client Protocol 2.0.50113.0)  
Content-Type: text/xml; charset=utf-8  
SOAPAction: ""  
Host: <servername>:<port 
Content-Length: 779  
Expect: 100-continue  
Accept-Encoding: gzip 
Code language: PHP (php)

Notice, that there is no Authentication item even though PreAuthenticate is set to true.

The reply back from WebMethods is as follows:

HTTP/1.0 500 Internal Server Error  
Set-Cookie: ssnid=11747k5Rwchr3vW0s23vcaCP1wCA2NDc=555590; path=/;  
Content-Type: text/xml;charset=utf-8  
Connection: Keep-Alive  
Content-Length: 849 
Code language: HTTP (http)

The problem is that .NET is expecting a challenge response from WebMethods, specifically a 401 error of “Invalid credentials.”  However, if the client’s credentials are not specified (there is no Authentication part to the header) then WebMethods returns an HTTP 500 status code (Internal Server Error) indicating that the request could not be fulfilled.

To fix the problem you can either change the .NET client or else the WebMethods server.  In my original posting, I demonstrated how to control the .NET client.  The result was an HTTP header that includes the Authentication portion as shown below:

POST /soap/rpc HTTP/1.1  
User-Agent: Mozilla/4.0 (compatible; MSIE 6.0; MS Web Services Client Protocol 2.0.50113.0)  
Authorization: BasicbGRwcm86bGRwcm8=  
Content-Type: text/xml; charset=utf-8  
SOAPAction: ""  
Host: spo-wm-py-srvr:5555  
Content-Length: 779  
Expect: 100-continue  
Accept-Encoding: gzip 
Code language: JavaScript (javascript)

However, it is also possible to change the WebMethods side (assuming you control that side) by creating an access-controlled SOAP processor that checks the credentials for each client request against a specified ACL and returns an HTTP 401 status code even if there are no credentials passed.

By the way, the tool I use for tracing HTTP is YATT.

Want More?

Check out this blog on fully-managed passwordless authentication!

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