Connect to a web service through a Proxy Server

Introduction

This article explains the how you access a webservice through a Proxy Server.

Using the code

In order to show an example of this, we will use a public web service provided by Google. To use this ws, we need to obtain a Validation Key from Google. Next we defined the search criteria and we display the total of obtained registries.

We use the following libraries :

NetworkCredential Class

Provides credentials for password-based authentication schemes such as basic, digest, NTLM, and Kerberos authentication. For a list of all members of this type, see NetworkCredential Members. The NetworkCredential class is a base class that supplies credentials in password-based authentication schemes such as basic, digest, NTLM, and Kerberos. Classes that implement the ICredentials interface, such as the CredentialCache class, return NetworkCredential instances. This class does not support public key-based authentication methods such as SSL client authentication.

WebProxy Class

Contains HTTP proxy settings for the WebRequest class. For a list of all members of this type, see WebProxy Members. The WebProxy class contains the proxy settings that WebRequest instances use to override the proxy settings in GlobalProxySelection. The WebProxy class is the base implementation of the IWebProxyinterface.

The Proxy Server IP Adress is 127,0,1,2 and the port is the 80. 
The data of the user for the authentication with the proxy are: 
User Id: user 
Password: pwd 
Domain: MyDomain 

The following VB.NET code shows an example:

' Search button: do a search, display number of results 
Private Sub btnSearch_Click(ByVal sender As System.Object, _
  ByVal e As System.EventArgs) Handles btnSearch.Click 

' Create a Google Search object 
Dim s As New Google.GoogleSearchService 

Try 

' google params 
Dim strLicenceseKey As String = "google license key" ' google license key 
Dim strSearchTerm As String = "Bruno Capuano" ' google license key 

' proxy settings 
Dim cr As New System.Net.NetworkCredential("user", "pwd", "MyDomain") 
Dim pr As New System.Net.WebProxy("127.0.1.2", 80) 

pr.Credentials = cr 
s.Proxy = pr 

' google search
Dim r As Google.GoogleSearchResult = s.doGoogleSearch(strLicenceseKey, _
  strSearchTerm, 0, 10, True, "", False, "", "", "")
' Extract the estimated number of results for the search and display it
Dim estResults As Integer = r.estimatedTotalResultsCount 

MsgBox(CStr(estResults))

Catch ex As System.Web.Services.Protocols.SoapException

MsgBox(ex.Message)

End Try

End Sub 

If you want to use the current user credential you can use the DefaultCredentials Property. The DefaultCredentials property applies only to NTLM, negotiate, and Kerberos-based authentication. Sample :

' set default credentials
pr.Credentials = System.Net.CredentialCache.DefaultCredentials 

DefaultCredentials represents the system credentials for the current security context in which the application is running. For a client-side application, these are usually the Windows credentials (user name, password, and domain) of the user running the application. For ASP.NET applications, the default credentials are the user credentials of the logged-in user, or the user being impersonated.

Note - The ICredentials instance returned by DefaultCredentials cannot be used to view the user name, password, or domain of the current security context.

Conclusion

This is my first article and a very simple one. Any questions or suggestions are welcome ! Bye !

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