If several schemes are returned in the WWW-Authenticate or Proxy-Authenticate header, this parameter defines which authentication schemes takes precedence over others. The first item in the collection represents the most preferred authentication scheme , the last item represents the ID of the least preferred one.

Also see:

org.apache.commons.httpclient.params.DefaultHttpParams

 public static synchronized AuthScheme getAuthScheme(String id) throws IllegalStateException 
{
        if (id == null) {
            throw new IllegalArgumentException("Id may not be null");
        }
        Class clazz = (Class)SCHEMES.get(id.toLowerCase());
        if (clazz != null) {
            try {
                return (AuthScheme)clazz.newInstance();
            } catch (Exception e) {
                LOG.error("Error initializing authentication scheme: " + id, e);
                throw new IllegalStateException(id + 
                    " authentication scheme implemented by " +
                    clazz.getName() + " could not be initialized");
            }
        } else {
            throw new IllegalStateException("Unsupported authentication scheme " + id);
        }
}

Gets the authentication scheme with the given ID.

 public static synchronized List getDefaultAuthPrefs() 
{
        return (List)SCHEME_LIST.clone();
}

Returns a list containing all registered authentication schemes in their default order.

 public static synchronized  void registerAuthScheme(String id,
    Class clazz) 
{
                                                                                                          
         if (id == null) {
             throw new IllegalArgumentException("Id may not be null");
         }
        if (clazz == null) {
            throw new IllegalArgumentException("Authentication scheme class may not be null");
        }
        SCHEMES.put(id.toLowerCase(), clazz);
        SCHEME_LIST.add(id.toLowerCase());
}

Registers a class implementing an authentication scheme with the given identifier. If a class with the given ID already exists it will be overridden. This ID is the same one used to retrieve the authentication scheme from #getAuthScheme(String) .

Please note that custom authentication preferences, if used, need to be updated accordingly for the new authentication scheme to take effect.

 public static synchronized  void unregisterAuthScheme(String id) 
{
         if (id == null) {
             throw new IllegalArgumentException("Id may not be null");
         }
        SCHEMES.remove(id.toLowerCase());
        SCHEME_LIST.remove(id.toLowerCase());
}

Unregisters the class implementing an authentication scheme with the given ID.