Consuming Webservices over HTTPS (SSL)
When Webservices are used, a common concern is security: SOAP messages are transferred in plain text over the network, so anyone with a sniffer could intercept the SOAP message and read it. In my opinion this could happen also to binary data, but probably it requires a little bit more hacker skills. So a solution is to use HTTPS (SSL) instead of HTTP, so the communication is encrypted. To accomplish this, you need to get and install a certificate (issued by a Certificate Authority) on your webserver. In a production environment you would buy a certificate from Verisign or another well known CA, or you would install your own CA, which is a component of Windows Server. If you only want to play with HTTPS, SSL and certificates or your project is in the development phase, you can also generate a test certificate using the MakeCert.exe tool (included in the .NET Framework SDK). After that you have to add this certificate to a website in IIS, and set a port which HTTPS should use.
When you browse to a HTTPS site, you probably get a dialog
window asking you if you want to trust the certificate
provided by the webserver. So the responsibility of
accepting the certificate is handled by the user. Let's get
back to the webservice scenario, if you want to invoke a
webservice located on a webserver which uses SSL and HTTPS
there is a problem. When you make the call from code, there
is no dialog window popping up, and asking if you trust the
certificate (luckily because this would be pretty ugly in
server-side scenarios); probably you'll get following
exception:
An unhandled exception of type
'System.Net.WebException' occurred in system.dll
Additional information: The underlying connection was closed: Could not establish trust relationship with remote server.
But there is a solution for this problem, you can solve this
in your code by creating your own CertificatePolicy class
(which implements the
ICertificatePolicy interface). In this class you will have to write your own
CheckValidationResult function that has to return true or
false, like you would press yes or no in the dialog window.
For development purposes I've created the following class
which accepts all certificates, so you won't get the nasty
WebException anymore:
public class TrustAllCertificatePolicy :
System.Net.ICertificatePolicy
{
public
TrustAllCertificatePolicy()
{}
public bool CheckValidationResult(ServicePoint sp,
X509Certificate cert,WebRequest req, int
problem)
{
return true;
}
}
As you can see the CheckValidationResult function always
returns true, so all certificates will be trusted. If you
want to make this class a little bit more secure, you can
add additional checks using the X509Certificate parameter
for example. To use this CertificatePolicy, you'll have to
tell the ServicePointManager to use it:
System.Net.ServicePointManager.CertificatePolicy = new
TrustAllCertificatePolicy();
This must be done (one time during the application
life cycle) before making the call to your webservice.