Thursday, November 25, 2010

Fall 2010

Colors, Fall 2010, Vermont and Massachusetts.

Monday, November 15, 2010

Avoiding browser popup for 401

If you are writing a web application that consumes RESTful web services which enforce HTTP basic authentication, you may face a problem where the browser may pop up a dialog box on the authentication failure (HTTP status: 401) before even your error handler code is called. This happens especially when the web application does not have any controller on the server side. For example, an application written using a client-side JavaScript framework such as Ext-JS.

The browser's HTTP user-agent obviously follows the HTTP protocol which says the following for 401.
The request requires user authentication. The response MUST include a WWW-Authenticate header field (section 14.47) containing a challenge applicable to the requested resource.

14.47 WWW-Authenticate

The WWW-Authenticate response-header field MUST be included in 401 (Unauthorized) response messages. The field value consists of at least one challenge that indicates the authentication scheme(s) and parameters applicable to the Request-URI.

where the contents of a challenge may itself contain a comma-separated list of authentication parameters. The authentication parameter realm is defined for all authentication schemes:

With some trial and error, we found that the pop up is triggered not due to the presence of 401 but due to the presence of the challenge.

So, as a web service developer, if you want to help service consumers disable the pop up and still send 401, you could use a trick. Replace Basic with your own scheme, e.g. xBasic as shown below.

To do this with Spring Security, you would want to override the commence method of the default

Write your own entry point, e.g. MyBasicAuthenticationEntryPoint as shown below.

Then plugin your entry point into the basic authentication filter as follows:

Thanks to Venkat Mantirraju in helping figure this out.