Thursday, 16 September 2010

Enabling Custom Username/Password Authentication WCF in IIS

A couple of posts back I was bemoaning the inability to use custom username/password authentication for all endpoints (WsHttp, BasicHttp and WebHttp) for a WCF service hosted in IIS.  The problem arises when you get to the WebHttp binding, because you can’t use message-level authentication (since it’s just a JSON packet), therefore you have to use Transport-level authentication.  Then you get to the biggest issue - that using Transport-level means having to use Basic/Windows/Digest authentication and IIS always automatically intercepts those authentication headers and attempts to authenticate to the server’s default windows account store (typically the domain it’s on, or it’s own local user store).

In this case, even if you configure your Custom UserName Password validator, it’ll never fire.

My solution to do a full, roll-your-own solution using Message Inspectors etc.  This still wouldn’t have solved the JSON problem fully, but it did mean that I could use my own Http headers to transmit my secure credentials.

I had a thought, though – what if IIS’ authentication could be extended, so that Basic authentication headers could be used on a per-endpoint basis (meaning that I was still free to use message-level for SOAP and Ws-Http if need-be)?

My initial google results were poor, and so I decided to use the MSDN Forums to get some ideas.  Needless to say – the answer that Marco Zhou has been exactly the thing I was looking.  All I did was to download the source for the excellent CustomBasicAuth project from CodePlex, and by following Dominick’s walkthrough was then able to extrude my own implementation that I could then plug into any WCF service.

The extra upshot of doing all this was that I can now use Role-based security on all my WCF methods, and the client just has to know how to send the credentials according to the type of endpoint they are using.  With the JSON endpoints I’m using the trick I posted earlier on how to intercept web service calls from Asp.Net Ajax client code in order to inject extra headers, but with the SOAP endpoints (currently from Silverlight) I’m using message-level headers and a Message Inspector (TIP – if you follow the CustomBasicAuth walkthrough exactly, you’ll add an Authorization provider to your WCF service.  If you then implement a message inspector to extract authentication details from a SOAP message, you can set the current Principal in that code – but here’s the beauty of it – it happens before WCF security kicks in, so the same Authorization provider will also work!).

So while it is a bit of a pain – once you’ve got the skeleton up and running, it’s actually pleasingly simple.

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