==== Error Handling

{{book.project.name}} has some error handling facilities for servlet based client adapters.
When an error is encountered in authentication, the client adapter will call `HttpServletResponse.sendError()`.
You can set up an `error-page` within your `web.xml` file to handle the error however you want.
The client adapter can throw 400, 401, 403, and 500 errors.


[source,xml]
----
<error-page>
    <error-code>403</error-code>
    <location>/ErrorHandler</location>
</error-page>
----    

The client adapter also sets an `HttpServletRequest` attribute that you can retrieve.
The attribute name is `org.keycloak.adapters.spi.AuthenticationError`.
Typecast this object to: `org.keycloak.adapters.saml.SamlAuthenticationError`.
This class can tell you exactly what happened.
If this attribute is not set, then the adapter was not responsible for the error code. 


[source,javascript]
----
public class SamlAuthenticationError implements AuthenticationError {
    public static enum Reason {
        EXTRACTION_FAILURE,
        INVALID_SIGNATURE,
        ERROR_STATUS
    }

    public Reason getReason() {
        return reason;
    }
    public StatusResponseType getStatus() {
        return status;
    }
}
----